Epidemiology

Cancers of the anal region account for <1% of gastrointestinal tumours and <3% of all new cancer diagnoses.[4]

It is estimated that there will be 10,540 new cases of cancers of the anus, anal canal, and anorectum in the US in 2024 and approximately 2190 deaths. Two-thirds of the new cases are expected to occur in women.[5]​​

At least 80% of patients have squamous cell carcinomas.[6][7] Approximately 15% of patients have adenocarcinomas.[6] These have a similar natural history to that of rectal cancer and are treated in a similar way.[8] 

For treatment of rectal cancer, see Colorectal cancer.

The incidence of squamous cell carcinoma of the anus (SCCA) is increasing. One study reported an increase in incidence of SCCA in the US of 2.9% per year between 2000 and 2011.[6] The incidence rate for anal adenocarcinoma remained static during the same period. Another study reported an increase in incidence of SCCA of 2.7% per year between 2001 and 2015, with marked increases in incidence in people aged 50 years and older.[9]

In the UK, the annual incidence is 1 per 100,000, with approximately 500 new cases per year.[10]

Human papillomavirus (HPV) is detectable in 95% of SCCAs.[11] Immunosuppression likely facilitates persistent anal HPV infection, leading to increased cancer risk. There is a clear association between HIV and anal canal cancer. People living with HIV have a 19-fold increased incidence of anal cancer, compared with people without HIV.[12] Incidence increases with age and is highest in men who have sex with men and people with AIDS.[12][13]

Solid organ transplant recipients have a 6.8-fold increased incidence of anal cancer, compared with the general population.[14] Patients with haematological malignancies and some autoimmune diseases (Crohn's disease, psoriasis, polyarteritis nodosa, and granulomatosis with polyangiitis), also have a higher risk of SCCA compared with the general population.[13][15]

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