Screening for anal intraepithelial neoplasia and prevention of anal cancer

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Incidence of anal and anal canal cancer

Squamous cell carcinoma of the anus and anal canal has a low incidence in the general population (1-2/100,000 people-year). However, when associated with risk factors such as co-infection with HIV, men who have sex with men (MSM), presence of high-grade lesions or carcinoma in the genitals and immunosuppression, this risk can increase considerably:

Anus and anal canal cancer can be screened with a complete proctological examination, with inspection and rectal touch, followed by anoscopy with biopsy in suspicious lesions (3).

High-grade anal intraepithelial lesions (high-grade AIN), as occurs in the cervix, can be identified through exams such as oncotic cytology or genotyping for high-risk oncogenic HPV obtained through the anal smear (Anal-Pap).

When these results come altered, the patient should be referred for a high-resolution anoscopy examination or anoscopy with image magnification, which resembles a colposcopy examination of the anus and anal canal region. Through this examination, it is possible to identify lesions suspicious for high-grade AIN, which, when identified through a biopsy, should be treated, through chemical cauterization or electrocautery or with infrared laser (4)

ANCHOR trial

• Until recently, there was not a robust degree of evidence to indicate the screening and treatment of high-grade anal intraepithelial lesions as a method of prevention for anal and anal canal cancer (2).
• However, in 2022 the results of the ANCHOR trial, (Anal Cancer HSIL Outcomes Research) (5) a prospective multicenter randomized study that evaluated 4446 people living with HIV who were followed up with cytology exams and high-resolution anoscopy were published in the NEJM.
• When high-grade anal intraepithelial lesions (AIN 2 p16+ or AIN3) were identified, the participants were randomized into two groups: one in which these lesions would be treated and another in which these lesions would be followed up every 6 months.
• The rate of progression to anal cancer was 53% lower in the treated group than in the group only followed up (p= 0.03).

Conclusion

• Anus and anal canal cancer is quite rare and should not be screened in the general population.
• Its incidence increases considerably in certain populations such as: people living with HIV, men who have sex with men, women with a history of cancer or high-grade lesions in the genitals and diseases or treatments that course with immunosuppression, which justifies screening in these groups.
• The identification and treatment of high-grade anal intraepithelial lesions in people living with HIV has proven effective in preventing anal and anal canal cancer.

References

1. Clifford, Gary M., et al. “A meta-analysis of anal cancer incidence by risk group: toward a unified anal cancer risk scale.” International journal of cancer 148.1 (2021): 38-47.
2. Stewart, David B., et al. “The American Society of Colon and Rectal Surgeons clinical practice guidelines for anal squamous cell cancers (revised 2018).” Diseases of the Colon & Rectum 61.7 (2018): 755-774.
3. Hillman, Richard John, et al. “International Anal Neoplasia Society guidelines for the practice of digital anal rectal examination.” Journal of lower genital tract disease 23.2 (2019): 138-146.
4. Hillman, Richard John, et al. “2016 IANS international guidelines for practice standards in the detection of anal cancer precursors.” Journal of lower genital tract disease 20.4 (2016): 283-291
5. Palefsky, Joel M., et al. “Treatment of anal high-grade squamous intraepithelial lesions to prevent anal cancer.” New England Journal of Medicine 386.24 (2022): 2273-2282.

How to cite this article

Ribeiro VL. Screening of anal intraepithelial neoplasia and prevention of anal cancer. Gastropedia 2023, vol. 1. Available at: https://gastropedia.com.br/sem-categoria/rastreamento-de-neoplasia-intrapeitelial-anal-e-prevencao-de-cancer-de-anus/