Anal cancer risk
The most important article I can recommend about the epidemiology of anal cancer is Clifford et al’s 2021 meta-analysis. The following figure illustrates the relative risk of anal cancer among different populations very nicely. For the sake of comparison, breast cancer incidence is around 127 per 100,000 person-years, colon cancer incidence is around 37, and lung around 50. (Statistics from SEER)
How to perform a proper digital ano-rectal examination (DARE)
A properly-performed anal examination, including visual inspection and DARE, is extremely sensitive for early anal cancer, and can be truly life-saving. The International Anal Dysplasia Society has a great document that describes how to perform a DARE, what to look for (both benign and malignant) when examining a patient.