Anal Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI]

Overview

Note: The Overview section summarizes the published evidence on this topic. The rest of the summary describes the evidence in more detail.

Another PDQ summary on Anal Cancer Treatment is also available.

Who Is at Risk?

Human papillomavirus (HPV) infection is the strongest risk factor for anal cancer and is accepted as a causal agent of squamous cell carcinoma of the anus and its precursor lesions.[1] Behaviors or medical conditions that either indicate HPV infection or facilitate HPV transmission or persistence are associated with increased risk. These behaviors and conditions include a history of HPV-related cancers, high-risk sexual practices such as sex between men, receptive anal intercourse and numerous sexual partners, human immunodeficiency virus (HIV) infection, and chronic immunosuppressive states.[2] Cigarette smoking is also a risk factor.[3]

Factors Associated With Increased Risk of Anal Cancer

Anal HPV infection

Based on solid evidence, HPV infection causes squamous cell carcinoma of the anus.

Magnitude of Effect: About 90% of anal squamous cell cancers occur in individuals with detectable HPV infection.[4] Of those, HPV strain 16 (HPV-16) and/or HPV-18 are detectable in more than 90% of cases.[4] Eighty-five percent of anal cancers have squamous cell histology.[2]

Study Design: Case series in men and women (HPV typing of tumor tissue).

Internal Validity: Good.

Consistency: Good.

External Validity: Good.

Behaviors or medical conditions associated with HPV infection

Based on solid evidence, behaviors or medical conditions that either indicate HPV infection or facilitate HPV transmission or persistence increase the risk or are associated with increased risk of anal cancer.

Magnitude of Effect: Risk varies by behavior and medical condition.

• History of cervical, vaginal, and vulvar cancer increases risk at least threefold.[5,6,7,8]
• High-risk sexual practices increase risk at least twofold, higher for individuals with many sexual partners and those who engage in receptive anal intercourse.[3,9,10,11]
• Chronic immunosuppressive states increase risk about 30-fold for individuals who are HIV positive, and risk is much higher for men who both are HIV positive and have sex with men.[12]
• Risk is at least threefold higher for organ transplant recipients.[11]

  Study Design: Cohort, cancer registries, case-control studies.

  Internal Validity: Good.

  Consistency: Good.

  External Validity: Good.

Cigarette smoking

Based on solid evidence, cigarette smoking increases the risk of anal cancer.

Magnitude of Effect: Risk is about twofold to threefold for ever-smokers; current smokers are at higher risk.[3,11,13]

Study Design: Cohort, case-control studies.

Internal Validity: Good.

Consistency: Good.

External Validity: Good.

Interventions Associated With a Decreased Risk of Anal Cancer

HPV vaccination

Based on solid evidence, HPV vaccination of men aged 16 to 26 years who have sex with men in the year before vaccination reduces anal intraepithelial neoplasia (AIN), a precursor lesion of anal cancer.

Magnitude of Effect: Vaccine efficacy against HPV-6, -11, -16, or -18–related AIN is between 50% and 75%.[14] Among those individuals who were naïve to vaccine types, incident quadrivalent HPV-type–associated anal low-grade squamous cell intraepithelial lesions (LSIL)/high-grade squamous cell intraepithelial lesions (HSIL) were not detected. In comparison, 11.1, 2.2, 4.5, and 2.8 cases per 100 person-years were reported for HPV-6, -11, -16, and -18–associated LSIL/HSIL, respectively, among those who were previously exposed to that respective HPV-type.[15]

Study Design: Randomized controlled trial, phase II open-label study.

Internal Validity: Good.

Consistency: Not applicable (N/A)—only one study.

External Validity: Good.

Based on national population-level observational data trends, HPV vaccination appears to decrease the risk of anal carcinoma in situ and invasive anal cancer among individuals aged 20 to 44 years after 2008 (when HPV vaccines were widely available).

Magnitude of Effect: Although direct efficacy of the HPV vaccine could not be measured in this population-level analysis, results showed a statistically significant decrease in the incidence of both anal carcinoma in situ (24% decrease) and invasive anal cancer (15% decrease). Older age groups (>45 years) who were not eligible for the HPV vaccine demonstrated increased HPV incidence after 2008.[16]

Study Design: National population-level cancer data.

Internal Validity: Good.

Consistency: Data from other HPV-related cancers, including population-level cervical cancer data, have shown similar decreases in overall cervical cancer incidence.

External Validity: Good.

Screening with high-resolution anoscopy (HRA) and treatment for high-grade squamous intraepithelial lesions (HSIL)

Utilizing data from a cohort of 28,175 individuals undergoing treatment for HIV in the Netherlands, anal cancer incidence significantly decreased over time. In a subcohort of 3,866 men who have sex with men (MSM) and had HRA-based anal cancer screening at least once, anal cancer mortality decreased by 31% when compared with those who did not participate in anal cancer screening (even after controlling for CD4 count less than 200).

Even though people living with HIV represent a high-risk population, anal cancer is still rare, and there were few anal cancers in this cohort, rendering conclusions difficult. In particular, there were only 37 anal cancers in men who do not have sex with men and only 10 among women. As a result, confidence intervals (CIs) were wide, and conclusions were suggestive at best.

Magnitude of Effect: Although direct efficacy of screening with HRA could not be measured in this cohort study, it found a statistically significant decrease in anal cancer mortality from 24% in the unscreened population to 3.7% in the screened population.

Study Design: Retrospective observational.

Internal Validity: Fair.

Consistency: Good.

External Validity: Fair.

Treatment of anal HSIL

Based on solid evidence, treating anal HSIL prevents anal cancer in HIV-positive individuals older than 35 years. When compared with the active monitoring arm, active HSIL treatment was associated with a decreased progression to anal cancer incidence by 57%.[17]

Study Design: Randomized phase III clinical trial.

Internal Validity: Good.

Consistency: N/A—only one study.

External Validity: Fair.

Interventions With Inadequate Evidence as to Whether They Reduce the Risk of Anal Cancer

Condom use

In a study of HPV transmission, MSM, recently had anal sex, and never use condoms were more likely to be infected with oncogenic HPV strains than were those who always used condoms. However, the association was not statistically significant.

Magnitude of Effect: About twofold but not statistically significant (odds ratio, 1.81; 95% CI, 0.58–5.68).[18]

Study Design: Case-control study.

Internal Validity: Fair.

Consistency: N/A—only one study.

External Validity: Fair.

References:

1. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans: Human papillomaviruses. IARC Monogr Eval Carcinog Risks Hum 90: 1-636, 2007.
2. Zandberg DP, Bhargava R, Badin S, et al.: The role of human papillomavirus in nongenital cancers. CA Cancer J Clin 63 (1): 57-81, 2013.
3. Daling JR, Madeleine MM, Johnson LG, et al.: Human papillomavirus, smoking, and sexual practices in the etiology of anal cancer. Cancer 101 (2): 270-80, 2004.
4. Parkin DM, Bray F: Chapter 2: The burden of HPV-related cancers. Vaccine 24 (Suppl 3): S3/11-25, 2006.
5. Chaturvedi AK, Engels EA, Gilbert ES, et al.: Second cancers among 104,760 survivors of cervical cancer: evaluation of long-term risk. J Natl Cancer Inst 99 (21): 1634-43, 2007.
6. Hemminki K, Dong C, Vaittinen P: Second primary cancer after in situ and invasive cervical cancer. Epidemiology 11 (4): 457-61, 2000.
7. Ruth A, Kosary A, Hildesheim A: New malignancies following cancer of the cervix uteri, vagina, and vulva. In: Curtis RE, Freedman DM, Ron E, et al., eds.: New Malignancies Among Cancer Survivors: SEER Cancer Registries, 1973-2000. National Cancer Institute, 2006. NIH Pub. No. 05-5302, pp 207-30.
8. Saleem AM, Paulus JK, Shapter AP, et al.: Risk of anal cancer in a cohort with human papillomavirus-related gynecologic neoplasm. Obstet Gynecol 117 (3): 643-9, 2011.
9. Daling JR, Weiss NS, Hislop TG, et al.: Sexual practices, sexually transmitted diseases, and the incidence of anal cancer. N Engl J Med 317 (16): 973-7, 1987.
10. Frisch M, Glimelius B, van den Brule AJ, et al.: Sexually transmitted infection as a cause of anal cancer. N Engl J Med 337 (19): 1350-8, 1997.
11. van der Zee RP, Richel O, de Vries HJ, et al.: The increasing incidence of anal cancer: can it be explained by trends in risk groups? Neth J Med 71 (8): 401-11, 2013.
12. Silverberg MJ, Lau B, Justice AC, et al.: Risk of anal cancer in HIV-infected and HIV-uninfected individuals in North America. Clin Infect Dis 54 (7): 1026-34, 2012.
13. Nordenvall C, Nilsson PJ, Ye W, et al.: Smoking, snus use and risk of right- and left-sided colon, rectal and anal cancer: a 37-year follow-up study. Int J Cancer 128 (1): 157-65, 2011.
14. Palefsky JM, Giuliano AR, Goldstone S, et al.: HPV vaccine against anal HPV infection and anal intraepithelial neoplasia. N Engl J Med 365 (17): 1576-85, 2011.
15. Palefsky JM, Lensing SY, Belzer M, et al.: High Prevalence of Anal High-Grade Squamous Intraepithelial Lesions, and Prevention Through Human Papillomavirus Vaccination, in Young Men Who Have Sex With Men Living With Human Immunodeficiency Virus. Clin Infect Dis 73 (8): 1388-1396, 2021.
16. Berenson AB, Guo F, Chang M: Association of Human Papillomavirus Vaccination With the Incidence of Squamous Cell Carcinomas of the Anus in the US. JAMA Oncol 8 (4): 1-3, 2022.
17. Palefsky JM, Lee JY, Jay N, et al.: Treatment of Anal High-Grade Squamous Intraepithelial Lesions to Prevent Anal Cancer. N Engl J Med 386 (24): 2273-2282, 2022.
18. Nyitray AG, Carvalho da Silva RJ, Baggio ML, et al.: Age-specific prevalence of and risk factors for anal human papillomavirus (HPV) among men who have sex with women and men who have sex with men: the HPV in men (HIM) study. J Infect Dis 203 (1): 49-57, 2011.

Incidence, Mortality, and Survival

United States

The Surveillance, Epidemiology, and End Results (SEER) Program age-adjusted annual incidence rate of anal cancer in the United States for the period 2016 to 2020 was 1.9 cases per 100,000 persons per year, and the mortality rate was 0.3 cases per 100,000 persons per year. Incidence rates were slightly higher for women than for men (2.3 vs. 1.6 per 100,000 person-years, respectively), but mortality rates were about the same.[1] In 2024, it is estimated that 10,540 new cases of anal cancer will be diagnosed, and 2,190 deaths will be caused by this disease in the United States.[2] Incidence rates increased annually from 2010 to 2019 (average increase, 1.7%), and mortality rates increased annually over the same time period (average increase, 4.1%). All incidence and mortality increases were statistically different from zero.[3] The 5-year survival rate has remained fairly constant since 1975, and on the basis of data from 2012 to 2018, it was 70.1%.[1]

World

An estimated 27,000 new cases of anal cancer were diagnosed worldwide in 2008.[4] No global incidence rates, mortality rates, or survival statistics are available.

References:

1. National Cancer Institute: SEER Stat Fact Sheets: Anal Cancer. Bethesda, Md: National Cancer Institute. Available online. Last accessed March 6, 2024.
2. American Cancer Society: Cancer Facts and Figures 2024. American Cancer Society, 2024. Available online. Last accessed June 21, 2024.
3. Surveillance Research Program, National Cancer Institute: SEER*Explorer: An interactive website for SEER cancer statistics. Bethesda, MD: National Cancer Institute. Available online. Last accessed March 6, 2024.
4. Forman D, de Martel C, Lacey CJ, et al.: Global burden of human papillomavirus and related diseases. Vaccine 30 (Suppl 5): F12-23, 2012.

Histology

About 85% of anal cancers in the United States have squamous cell histology or a histological variant.[1] Nearly all other anal cancers are adenocarcinomas.[2] Human papillomavirus (HPV) vaccination, HPV screening, and screening for the presence of anal cancer precursor lesions will probably change the histological distribution of anal cancer in years to come, as HPV is implicated only in squamous cell carcinomas,[3] and identification of precursor lesions is expected to reduce invasive squamous cell disease.

Precursor Lesions

Squamous cell cancer of the anus is preceded by grade 2 or 3 anal intraepithelial neoplasia (AIN), also referred to as high-grade AIN. Grade 1 AIN is not considered a precursor lesion of anal cancer but may precede high-grade AIN.[4] The cytological terms for low- and high-grade AIN are low-grade squamous cell intraepithelial lesions (LSIL) and high-grade squamous cell intraepithelial lesions (HSIL).[4]

One study reported that 11% of AIN cases progressed to invasive disease over an 8-year period.[5] However, results from another study suggested that progression is much less frequent. Using AIN prevalence and anal cancer incidence data, the investigators estimated hypothetical annual rates of progression from high-grade AIN to anal cancer. For men who have sex with men (MSM) and who are human immunodeficiency virus (HIV) positive, the rate was about 1 case in 600 patients. For HIV-negative MSM, the rate was 1 case in 4,000 patients.[6] Using meta-analysis techniques to combine data from numerous studies worldwide, the investigators estimated that the prevalence of LSIL is 27.5% (95% confidence interval [CI], 21.9%–33.2%) and the prevalence of HSIL is 6.7% (95% CI, 4.4%–9.0%) in HIV-positive MSM. Among HIV-negative MSM, the prevalence of LSIL was 6.6% (95% CI, 1.1%–12.1%), and the prevalence of HSIL was 2.7% (95% CI, 0.0%–5.1%).[6]

References:

1. Zandberg DP, Bhargava R, Badin S, et al.: The role of human papillomavirus in nongenital cancers. CA Cancer J Clin 63 (1): 57-81, 2013.
2. Ries LAG, Young JL, Keel GE, et al., eds.: SEER Survival Monograph: Cancer Survival Among Adults: U. S. SEER Program, 1988-2001, Patient and Tumor Characteristics. National Cancer Institute, 2007. NIH Pub. No. 07-6215.
3. Joseph DA, Miller JW, Wu X, et al.: Understanding the burden of human papillomavirus-associated anal cancers in the US. Cancer 113 (10 Suppl): 2892-900, 2008.
4. Hoots BE, Palefsky JM, Pimenta JM, et al.: Human papillomavirus type distribution in anal cancer and anal intraepithelial lesions. Int J Cancer 124 (10): 2375-83, 2009.
5. Watson AJ, Smith BB, Whitehead MR, et al.: Malignant progression of anal intra-epithelial neoplasia. ANZ J Surg 76 (8): 715-7, 2006.
6. Machalek DA, Poynten M, Jin F, et al.: Anal human papillomavirus infection and associated neoplastic lesions in men who have sex with men: a systematic review and meta-analysis. Lancet Oncol 13 (5): 487-500, 2012.

Risk Factors

Factors Associated With Increased Risk of Anal Cancer

Anal HPV infection

Human papillomavirus (HPV) infection is the strongest risk factor for anal cancer. About 90% of anal cancers occur in individuals with detectable HPV infection.[1] HPV infection with oncogenic HPV strains is accepted as a causal agent and necessary condition for development of squamous cell carcinoma of the anus and its precursor lesions.[2] In a 2009 meta-analysis of about 1,000 invasive squamous cell lesions, HPV-16 was present in about two-thirds of lesions, and HPV-18 was present in about 5% of lesions.[3] Because 85% of anal cancers have a squamous cell carcinoma histology or a histological variant,[4] it is probable that elimination of oncogenic HPV infection would nearly eradicate anal cancer.

HPVs are typically cleared rapidly in healthy individuals. Persistence of the oncogenic HPV strains is more likely in individuals with compromised immune systems; therefore, the risk of squamous cell anal cancer is much higher in these individuals. Behaviors that facilitate transmission of HPVs also increase risk.[4] While these conditions or behaviors will probably have, at most, little independent effect on squamous cell anal cancer risk (that is, in the absence of HPV), data that fully address this hypothesis are very limited.

Given the paucity of cases of anal adenocarcinoma and other nonsquamous histological subtypes, it is unknown what role, if any, HPV plays in the development of these lesions.

Behaviors or medical conditions associated with HPV infection

History of cervical, vaginal, and vulvar cancer

Cancers of the cervix, vagina, and vulva are HPV-related cancers.[5] Long-term registry-based monitoring of cervical, vaginal, and vulvar cancer survivors demonstrates an increase in anal cancer risk for these individuals, although the magnitude of the relationship varies.[6,7,8,9] For survivors of invasive cervical cancer, the standardized incidence ratio (SIR) for anal cancer was 3.1 (95% confidence interval [CI], 1.9–4.9) in a cohort of more than 100,000 cervical cancer survivors from Denmark, Finland, Norway, Sweden, and the United States.[6] The SIR for anal cancer was 6.2 (95% CI, 4.1–8.7) for survivors of invasive cervical cancer in the Surveillance, Epidemiology, and End Results (SEER) Program registry data from 1973 to 2007 (more than 1 million person-years).[8] In the latter cohort, the SIR for women with in situ cervical cancer was 16.4 (95% CI, 13.7–19.2). In an analysis of data from the Swedish Family-Cancer Database, which used data from 1958 to 1996, SIRs were 3.8 (95% CI, 2.9–4.7) among the women with in situ cervical cancer and 3.9 (95% CI, 2.3–6.0) among the women with invasive cervical cancer.[8] In the aforementioned multicountry cohort,[6] the anal cancer SIRs for in situ and invasive vaginal cancer were 7.6 (95% CI, 2.4–15.6) and 1.8 (95% CI, 0.2–5.3), respectively; the anal cancer SIRs for in situ and invasive vulvar cancer were 22.2 (95% CI, 16.7–28.4) and 17.4 (95% CI, 16.7–28.4), respectively.

Individuals with cancer of the oropharynx [10] and penis,[11] two other HPV-associated cancers, are hypothesized to be at increased risk of anal cancer. From 1973 to 2007 (more than 1 million person-years),[7] it was estimated that the observed-to-expected ratio for anal cancer among people with oropharyngeal cancer was twofold (significantly different from one). In that same data source, it was also estimated that no anal cancers occurred after penile cancer, although the expected number of cases was 0.36.

HIV infection/AIDS

The association between HIV infection and anal cancer is strong. One meta-analysis indicated a 30-fold increase in anal cancer in HIV-infected people, compared with the general population (SIR, 28.8; 95% CI, 21.6–38.3).[12] A nationwide Danish cohort study with data from 1995 to 2009 observed an even stronger association (incidence rate ratio, 77.9; 95% CI, 36.2–167.7).[13] This association between HIV infection and anal cancer is confounded or modified by other factors associated with anal cancer, such as HPV status, high-risk behaviors, and level of immunocompromise. For example, the magnitude of the association between HIV infection and anal cancer risk varies by sexual preference. In one study,[14] the highest SIR and the highest incidence rate were observed for HIV-positive men who have sex with men (MSM), compared with HIV-negative men (SIR, 80.3; 95% CI, 42.7–151.1). The incidence rate for HIV-positive MSM is 131 cases per 100,000 person-years. The SIR for HIV-positive men who did not have sex with men was lower but nonnegligible (SIR, 26.7; 95% CI, 11.5–61.7; incidence rate, 46 cases per 100,000 person-years). In the same study, 30 of 8,842 HIV-positive women had anal cancer diagnoses (incidence rate, 2 cases per 100,000 person-years) but none of the 11,653 HIV-negative women were diagnosed with anal cancer; thus, no SIR could be calculated, and the incidence rate was zero. Among men with anal cancer, the Danish study observed a mortality rate ratio of 3.2 (95% CI, 1.1–9.2) for HIV-positive men compared with men in the general population.[13]

Anal HPV infection is common in HIV-positive individuals. Studies suggest an HPV prevalence of 85% to 95% among HIV-positive MSM, 76% to 90% in HIV-positive women, and 60% in HIV-positive heterosexual men.[14]

In a cohort of almost 7,000 men with AIDS, 28 anal cancers occurred, and the odds ratios (OR) suggested relatively modest elevations (about twofold) in risk as the prevalence of high-risk behaviors increased. However, the only statistically significant OR relating to sexual practices was for seven or more unprotected anal receptive sexual partners during the time between study onset and the third study visit (OR, 4.0; 95% CI, 1.1–14.6).[15] In a cohort of nearly half a million AIDS patients, intravenous drug use was associated with anal cancer (SIR, 11.7; 95% CI, 4.2–25.5 for men and SIR, 38.0; 95% CI, 10.3–97.3 for women).[16] Current cigarette smoking, relative to never smoking, has also been observed to increase anal cancer risk in HIV-positive individuals (OR, 2.6; 95% CI, 1.3–5.3).[17]

Anal cancer risk is positively associated with severity of immunosuppression in HIV-positive and AIDS patients.[14] When combined antiretroviral therapy (cART) became available in 1996, the incidence of anal cancer among these patients was expected to decrease. While decreases have been observed for other HIV-associated cancers, such trends have not been observed for anal cancer. It has been proposed that timing of cART treatment influences the risk of anal cancer, and that to be effective against anal cancer, cART must be administered to those with HPV infection earlier in the course of infection than has been clinically practiced.[18] One study suggests that immunosuppression levels 6 to 7 years before anal cancer diagnosis may be more strongly associated with odds of developing the disease than immunosuppression levels in the 12 months before anal cancer diagnosis.

Investigators reported ORs for CD4+ counts 6 to 7 years before anal cancer diagnosis as follows:[17]

• For counts of 350 to 499: OR, 2.8 (95% CI, 0.6–13.0).
• For counts of 200 to 349: OR , 5.9 (95% CI, 1.5–23.0).
• For counts lower than 200: OR, 14.0 (95% CI, 3.9–50.9).

ORs for CD4+ counts in the 12 months before diagnosis were as follows:

• For counts of 350 to 499: OR, 2.0 (95% CI, 0.9–4.6).
• For counts of 200 to 349: OR, 2.2 (95% CI, 1.1–4.6).
• For counts lower than 200: OR, 4.6 (95% CI, 1.8–11.4).

Similar patterns were observed for CD8+ cell counts and for CD4+/CD8+ ratios.

Sexual practices associated with increased risk

Sexual practices that confer elevation in anal cancer risk include receptive anal intercourse, numerous sexual partners, and sex between men.[19] These are practices that are known or believed to increase anal exposure to oncogenic strains of HPV. Because HPV and HIV infection are highly correlated with high-risk sexual practices, few data exist that assess the independent effects of sexual behaviors. Before the HIV/AIDS era, the epidemiology of anal cancer received little attention; it was only as the concurrent emergence of AIDS and the increase in anal cancer occurred that sexual practices were investigated as possible risk factors.

Regardless of the underlying reason, MSM have the highest rates of anal cancer when compared with other men and women. As previously mentioned, HIV-positive MSM have the highest anal cancer rates (about 50 cases per 100,000 person-years),[20] but HIV-negative MSM have significantly higher rates than do men in the general population; their incidence is estimated to be 5 cases per 100,000 person-years.[20] Case-control studies have observed a modest (about twofold) increase in risk for women who practice receptive anal intercourse;[21,22] however, one study found the association to exist only among women who first had anal intercourse before age 30 years (OR, 3.4; 95% CI, 1.7–6.6).[21] In the same study, adjusted ORs for both men and women increased with increasing lifetime number of sexual partners. The OR associated with 10 or more partners was 4.5 (95% CI, 2.7–7.4) for women and 2.5 (95% CI, 1.1–5.5) for men. Increased risk for both men and women has been observed with a history of anal warts and certain other sexually transmitted diseases.[21]

Chronic immunosuppressive states other than HIV infection

Chronic immunosuppression in general is thought to increase risk of anal cancer because of its impact on the ability to clear HPV infection.[19] Organ transplant recipients are at elevated risk of anal cancer because immunosuppressant medications are used to prevent organ rejection. Three large transplant cohort studies have observed SIRs for anal cancer of 2.8 (95% CI, 1.5–4.6),[12] 5.8 (95% CI, 4.7–7.2),[23] and 10.3 (95% CI, 2.8–26.6).[12] Autoimmune disorders are hypothesized to increase risk of anal cancer because of the condition, the treatment, or both. However, the rarity of anal cancer and relative rarity of many of these disorders have led to conflicting findings or limited data. A cohort study of the Denmark National Patient Registry that included nearly 30 years' experience observed statistically significant threefold increases in risk for Crohn disease (SIR, 3.1; 95% CI, 1.2–6.4) and psoriasis (SIR, 3.1; 95% CI, 1.8–5.1), as well as a ninefold increase for polyarteritis nodosa (SIR, 8.8; 95% CI, 1.5–29.0) and a 12-fold increase in Wegener granulomatosis (SIR, 12.4; 95% CI, 2.1–40.8).[24]

Cigarette smoking

Cigarette smoking was among the first risk factors for anal cancer to be identified. In 1987, a case-control study of 58 men and 90 women observed a ninefold increase in risk (relative risk [RR], 9.4; 95% CI, 2.3–38.5) for men and an eightfold increase in risk for women (RR, 7.7; 95% CI, 3.5–17.2) for current smokers after adjustment for number of sexual partners.[25] RRs for former smokers were not statistically significant and less than twofold. Another case-control study of 306 patients suggested that current cigarette smoking may be an independent risk factor for anal cancer because adjustment for HPV status and number of sexual partners dampened but did not eliminate the significant associations observed in the 1987 study. The OR was 3.9 (95% CI, 1.9–8.0) for men and 3.8 (95% CI, 2.3–6.2) for women.[22] Given the rarity of anal cancer, studies have not been able to rigorously explore whether risk of anal cancer varies by other aspects of smoking history, such as pack-years smoked and time since cessation. The latter would be of particular interest, given the observation of strong risk in current smokers but no risk in former smokers.

References:

1. Parkin DM, Bray F: Chapter 2: The burden of HPV-related cancers. Vaccine 24 (Suppl 3): S3/11-25, 2006.
2. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans: Human papillomaviruses. IARC Monogr Eval Carcinog Risks Hum 90: 1-636, 2007.
3. Hoots BE, Palefsky JM, Pimenta JM, et al.: Human papillomavirus type distribution in anal cancer and anal intraepithelial lesions. Int J Cancer 124 (10): 2375-83, 2009.
4. Zandberg DP, Bhargava R, Badin S, et al.: The role of human papillomavirus in nongenital cancers. CA Cancer J Clin 63 (1): 57-81, 2013.
5. Forman D, de Martel C, Lacey CJ, et al.: Global burden of human papillomavirus and related diseases. Vaccine 30 (Suppl 5): F12-23, 2012.
6. Chaturvedi AK, Engels EA, Gilbert ES, et al.: Second cancers among 104,760 survivors of cervical cancer: evaluation of long-term risk. J Natl Cancer Inst 99 (21): 1634-43, 2007.
7. Saleem AM, Paulus JK, Shapter AP, et al.: Risk of anal cancer in a cohort with human papillomavirus-related gynecologic neoplasm. Obstet Gynecol 117 (3): 643-9, 2011.
8. Hemminki K, Dong C, Vaittinen P: Second primary cancer after in situ and invasive cervical cancer. Epidemiology 11 (4): 457-61, 2000.
9. Ruth A, Kosary A, Hildesheim A: New malignancies following cancer of the cervix uteri, vagina, and vulva. In: Curtis RE, Freedman DM, Ron E, et al., eds.: New Malignancies Among Cancer Survivors: SEER Cancer Registries, 1973-2000. National Cancer Institute, 2006. NIH Pub. No. 05-5302, pp 207-30.
10. Frisch M, Melbye M: Anal cancer. In: Schottenfeld D, Fraumeni JF Jr, eds.: Cancer Epidemiology and Prevention. 3rd ed. Oxford University Press, 2006, pp 830-40.
11. McMaster ML, Feuer EJ, Tucker MA: New malignancies following cancer of the male genital tract. In: Curtis RE, Freedman DM, Ron E, et al., eds.: New Malignancies Among Cancer Survivors: SEER Cancer Registries, 1973-2000. National Cancer Institute, 2006. NIH Pub. No. 05-5302, pp 257-84.
12. Grulich AE, van Leeuwen MT, Falster MO, et al.: Incidence of cancers in people with HIV/AIDS compared with immunosuppressed transplant recipients: a meta-analysis. Lancet 370 (9581): 59-67, 2007.
13. Legarth R, Helleberg M, Kronborg G, et al.: Anal carcinoma in HIV-infected patients in the period 1995-2009: a Danish nationwide cohort study. Scand J Infect Dis 45 (6): 453-9, 2013.
14. Silverberg MJ, Lau B, Justice AC, et al.: Risk of anal cancer in HIV-infected and HIV-uninfected individuals in North America. Clin Infect Dis 54 (7): 1026-34, 2012.
15. D'Souza G, Wiley DJ, Li X, et al.: Incidence and epidemiology of anal cancer in the multicenter AIDS cohort study. J Acquir Immune Defic Syndr 48 (4): 491-9, 2008.
16. Chaturvedi AK, Madeleine MM, Biggar RJ, et al.: Risk of human papillomavirus-associated cancers among persons with AIDS. J Natl Cancer Inst 101 (16): 1120-30, 2009.
17. Bertisch B, Franceschi S, Lise M, et al.: Risk factors for anal cancer in persons infected with HIV: a nested case-control study in the Swiss HIV Cohort Study. Am J Epidemiol 178 (6): 877-84, 2013.
18. Engels EA, Madeleine MM: Invited commentary: Biological and clinical insights from epidemiologic research into HIV, HPV, and anal cancer. Am J Epidemiol 178 (6): 885-7, 2013.
19. van der Zee RP, Richel O, de Vries HJ, et al.: The increasing incidence of anal cancer: can it be explained by trends in risk groups? Neth J Med 71 (8): 401-11, 2013.
20. Machalek DA, Poynten M, Jin F, et al.: Anal human papillomavirus infection and associated neoplastic lesions in men who have sex with men: a systematic review and meta-analysis. Lancet Oncol 13 (5): 487-500, 2012.
21. Frisch M, Glimelius B, van den Brule AJ, et al.: Sexually transmitted infection as a cause of anal cancer. N Engl J Med 337 (19): 1350-8, 1997.
22. Daling JR, Madeleine MM, Johnson LG, et al.: Human papillomavirus, smoking, and sexual practices in the etiology of anal cancer. Cancer 101 (2): 270-80, 2004.
23. Engels EA, Pfeiffer RM, Fraumeni JF, et al.: Spectrum of cancer risk among US solid organ transplant recipients. JAMA 306 (17): 1891-901, 2011.
24. Sunesen KG, Nørgaard M, Thorlacius-Ussing O, et al.: Immunosuppressive disorders and risk of anal squamous cell carcinoma: a nationwide cohort study in Denmark, 1978-2005. Int J Cancer 127 (3): 675-84, 2010.
25. Daling JR, Weiss NS, Hislop TG, et al.: Sexual practices, sexually transmitted diseases, and the incidence of anal cancer. N Engl J Med 317 (16): 973-7, 1987.

Interventions Associated With a Decreased Risk of Anal Cancer

HPV Vaccination

Because human papillomavirus (HPV) is a causal condition for squamous cell anal cancer development, vaccination against the oncogenic strains of HPV before exposure may reduce the risk of anal cancer. Conducted from 2004 to 2008, a multicountry trial randomly assigned 4,065 boys and men to receive either the three-shot quadrivalent HPV vaccine regimen (for HPV-6, -11, -16, and -18) or a three-shot placebo injection regimen. Of the 4,065 patients, 602 reported having sex with male partners in the year before enrollment. Heterosexual participants were between the ages of 16 years and 23 years and had no more than five lifetime female partners. Patients who reported sex with male partners were between the ages of 16 years and 26 years and had no more than five lifetime male or female partners. Persistent infection was defined as detection of the same HPV type in anogenital swabs or biopsy specimens collected on two or more consecutive visits, with an interval of 6 months between visits. In the intent-to-treat analysis, which included participants regardless of their baseline HPV status, the efficacy against persistent HPV-6, -11, -16, and -18 infection was 48% (95% confidence interval [CI], 36.0%–57.6%). Among those who were negative for the four HPV strains of interest at baseline (per the protocol analysis, which included 1,397 intervention-arm and 1,408 control-arm participants), vaccine efficacy against persistent HPV-6, -11, -16, and -18 infection was 90% (95% CI, 69.2%–98.1%).[1]

A nonrandomized, phase II, open-label trial (AMC 072 [NCT01209325]) was conducted in 149 men who have sex with men living with HIV. This study did not show a statistically significant difference between incident-persistent infections in the naïve, per-protocol, and previously exposed per-protocol groups. However, there was a statistically significant reduction in incident HPV-16–associated histological high-grade squamous intraepithelial lesions (HSIL) in the naïve group when compared with the previously exposed group (P = .014). The authors conducted a secondary analysis that compared the per-protocol quadrivalent HPV (qHPV)-type naïve participants in the AMC 072 trial to the original, per-protocol placebo group in the Merck 020 trial. This analysis demonstrated that vaccinated qHPV-naïve AMC-072 participants had significantly reduced disease in a combined analysis of all four qHPV types (5.8 per 100 person-years vs. 0 per 100 person-years; P = .008).[2]

Among the 602 patients who had sex with men, the vaccine efficacy against persistent HPV-6, -11, -16, and -18 infection was 59% (95% CI, 43.0%–71.4%) in the intent-to-treat analysis and 95% (95% CI, 80.4%–99.4%) in the per-protocol analysis. Efficacy against HPV-6, -11, -16 or -18–associated anal intraepithelial neoplasia (AIN) was 50% (95% CI, 25.7%–67.2%) in the intention-to-treat analysis and 77.5% (95% CI, 39.6%–93.9%) in the per-protocol analysis (275 intervention-arm and 276 control-arm participants). Efficacy against HPV-6, -11, -16, or -18–associated high-grade AIN was 54.2% (95% CI, 18.0%–75.3%) in the intent-to-treat analysis and 74.9% (95% CI, 8.8%–95.4%) in the per-protocol analysis (194 intervention-arm and 208 control-arm participants).[3]

Efficacy of the bivalent (HPV-16 and HPV-18) vaccine against anal infection was evaluated in the context of a randomized controlled trial of cervical cancer prevention. Conducted in 6,300 Costa Rican women aged 18 to 25 years at enrollment, the trial compared the efficacy of the three-dose bivalent vaccine with that of a control vaccine. Four years after vaccination, most women were offered the option of providing an anal specimen. Among the 2,103 intervention-arm and 2,107 control-arm participants who provided specimens, vaccine efficacy (i.e., absence of HPV-16 or -18 in the specimen) was 62% (95% CI, 47.1%–73.1%). Among the 1,003 intervention-arm and 986 control-arm participants who provided anal specimens, received the three doses, had no evidence of cervical HPV-16 or -18 infection before vaccination, and were seronegative before vaccination, vaccine efficacy was 84% (95% CI, 66.7%–92.8%).[4]

These data strongly suggest that vaccination against oncogenic HPV strains will lead to reductions in anal cancer. They also suggest that vaccination before exposure will provide the most benefit.

Treatment of Anal HSIL

Until the Anal Cancer–HSIL Outcomes Research (ANCHOR) trial was published, there had not been confirmation that treating anal HSIL decreased an individual's risk for invasive cancer.[5] However, the findings from the ANCHOR trial provided solid evidence that treatment of anal HSIL prevented the incidence of anal cancer. This trial, which was a phase III trial conducted at 25 U.S. sites, included individuals living with HIV who were aged 35 years or older and had biopsy-proven anal HSIL. Participants were randomly assigned in a 1:1 ratio to receive either HSIL treatment or active monitoring without treatment. Nine cases were diagnosed in the treatment group (173 per 100,000 person-years; 95% CI, 90.0–332.0), and 21 cases were diagnosed in the active-monitoring group (402 per 100,000 person-years; 95% CI, 262.0–616.0) after a median follow-up of 25.8 months. The rate of progression to anal cancer was 57% lower in the treatment group than it was in the active-monitoring group (95% CI, 6.0–80.0; P = .03 by log-rank test).

In a recent cohort study of 28,175 individuals being treated for HIV (59.7%, men who have sex with men [MSM]), 227 primary anal cancer cases were diagnosed.[6] Despite the increasing average age of the cohort, crude incidence rates of anal cancer in MSM declined slowly over time from 107.0 per 100,000 person-years (95% CI, 75.7–147.0) in 1996 to 2005 to 93.7 per 100,000 person-years (95% CI, 75.3–115.0) in 2013 to 2020 (P = .49). Crude incidence rates in men who do not have sex with men (non-MSM) and women were generally lower than those in MSM. However, crude incidence rates increased slightly over time from 51.08 per 100,000 person-years (95% CI, 20.54–105.25) to 67.82 per 100,000 person-years (95% CI, 40.83–105.91; P = .52) in non-MSM and from 8.09 per 100,000 person-years (95% CI, 0.20–45.06) to 24.95 per 100,000 person-years (95% CI, 10.03–51.40; P = .29) in women. In addition, the authors compared a subcohort of 3,866 MSM who received high-resolution anoscopy (HRA) screening at least once and treatment for HSIL. Furthermore, if screened individuals had low-grade squamous intraepithelial lesions (LSIL), they continued HRA screening once yearly, and those who had HSIL treatment received HRA screening every 6 months. TNM tumor staging was more favorable (Cochrane-Armitage test for trend, P = .033) in individuals diagnosed with anal cancer during screening. Crude anal cancer–associated 5-year mortality in people living with HIV decreased from 30.4% (1996–2005) to 18.3% (2013–2020; odds ratio, 0.48; P = .070). Anal cancer–related mortality was 3.7% (95% CI, 0.5–23.5) in all men who had been screened and 24.0% (95% CI, 18.1–31.3) in men who had not been screened (P = .023). In men, screening participation (hazard ratio [HR], 0.31; P = .051) and cumulative exposure to CD4 counts of less than 200 cells per µL (HR, 1.11 per year; P = .0022) were independently associated with anal cancer–related mortality.

Even though people living with HIV represent a high-risk population, anal cancer is still rare, and there were few anal cancers in this cohort, rendering conclusions difficult. In particular, there were only 37 anal cancers in non-MSM and only 10 among women. As a result, CIs were wide, and conclusions were suggestive at best. Of note, there are no known randomized controlled trials that provide evidence to support the conclusion of this study.

Data do not support the conclusion that men had improved survival when they were diagnosed with anal cancer after screening or that it is important to screen those who are at high risk of developing anal cancer. The study purported to show reduced mortality after an anal cancer diagnosis among screened men, but the curves in the study's results did not make adjustments for lead-time bias, selection bias, nor the possibility of overdiagnosis bias. The study also suggested that there was a larger proportion of early-stage cases among screened individuals, but the proportional stage shift caused by anal cancer screening is known to be influenced by lead-time and overdiagnosis biases. There was no mention of adjustment for these biases in the study's results. In addition, there was a high proportion of unknown stages, further suggesting that the conclusions in this study were not supported by the data. This is an additional rationale for why the data did not support the conclusion of the study.

References:

1. Giuliano AR, Palefsky JM, Goldstone S, et al.: Efficacy of quadrivalent HPV vaccine against HPV Infection and disease in males. N Engl J Med 364 (5): 401-11, 2011.
2. Palefsky JM, Lensing SY, Belzer M, et al.: High Prevalence of Anal High-Grade Squamous Intraepithelial Lesions, and Prevention Through Human Papillomavirus Vaccination, in Young Men Who Have Sex With Men Living With Human Immunodeficiency Virus. Clin Infect Dis 73 (8): 1388-1396, 2021.
3. Palefsky JM, Giuliano AR, Goldstone S, et al.: HPV vaccine against anal HPV infection and anal intraepithelial neoplasia. N Engl J Med 365 (17): 1576-85, 2011.
4. Kreimer AR, González P, Katki HA, et al.: Efficacy of a bivalent HPV 16/18 vaccine against anal HPV 16/18 infection among young women: a nested analysis within the Costa Rica Vaccine Trial. Lancet Oncol 12 (9): 862-70, 2011.
5. Palefsky JM, Lee JY, Jay N, et al.: Treatment of Anal High-Grade Squamous Intraepithelial Lesions to Prevent Anal Cancer. N Engl J Med 386 (24): 2273-2282, 2022.
6. van der Zee RP, Wit FWNM, Richel O, et al.: Effect of the introduction of screening for cancer precursor lesions on anal cancer incidence over time in people living with HIV: a nationwide cohort study. Lancet HIV 10 (2): e97-e106, 2023.

Interventions With Inadequate Evidence as to Whether They Reduce the Risk of Anal Cancer

Condom Use

Because human papillomavirus (HPV) can be transmitted through microabrasions, as well as through more pronounced exposures such as exchange of certain bodily fluids,[1] restriction of condom use to penetrative activity will not protect against transmission that occurs as part of other sexual contact. Nevertheless, condom use would be expected to reduce some risk of transmission and thus anal cancer risk. Few data that explore these hypotheses exist, and those that do suggest a very modest effect, if any. Of note, the ability of condom use to reduce cervical cancer risk is still uncertain and the subject of debate.[2]

In an Italian cohort of 258 HIV-negative men who have sex with men (MSM), the odds ratio (OR) for infection with high-risk HPV strains was 1.7 (95% confidence interval [CI], 0.52–6.3) for inconsistent or no use of condoms in receptive anal sex, compared with consistent condom use.[3] In a Brazilian cohort that included 176 MSM, the OR for oncogenic HPV infection was 1.8 (95% CI, 0.77–4.35) for men who sometimes used condoms for anal sex and 1.8 (95% CI, 0.58–5.68) for men who never used condoms, compared with men who always used condoms.[4]

References:

1. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans: Human papillomaviruses. IARC Monogr Eval Carcinog Risks Hum 90: 1-636, 2007.
2. Chelimo C, Wouldes TA, Cameron LD, et al.: Risk factors for and prevention of human papillomaviruses (HPV), genital warts and cervical cancer. J Infect 66 (3): 207-17, 2013.
3. Donà MG, Palamara G, Di Carlo A, et al.: Prevalence, genotype diversity and determinants of anal HPV infection in HIV-uninfected men having sex with men. J Clin Virol 54 (2): 185-9, 2012.
4. Nyitray AG, Carvalho da Silva RJ, Baggio ML, et al.: Age-specific prevalence of and risk factors for anal human papillomavirus (HPV) among men who have sex with women and men who have sex with men: the HPV in men (HIM) study. J Infect Dis 203 (1): 49-57, 2011.

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This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about anal cancer prevention. It is intended as a resource to inform and assist clinicians in the care of their patients. It does not provide formal guidelines or recommendations for making health care decisions.

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PDQ® Screening and Prevention Editorial Board. PDQ Anal Cancer Prevention. Bethesda, MD: National Cancer Institute. Updated <MM/DD/YYYY>. Available at: https://www.cancer.gov/types/anal/hp/anal-prevention-pdq. Accessed <MM/DD/YYYY>. [PMID: 26389511]

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Last Revised: 2024-03-06