This can be uncomfortable, but should not hurt.
Anal Cancer Expanded Version
Cells on the surface layer of the anus look like cancer cells, but have not grown into deeper layers of the anus. It is unclear how successful these screening tests, and any subsequent treatments, are at preventing cancers or saving lives from the prevention of anal cancer, but this likelihood is thought to be very similar to the improvements found with the use of cervical cancer screening in women using the pelvic exam Pap test. They compare standard treatments with others that may be better. Clinical trials can be found online at NCI's website.