New Treatments for Anal Cancer
Tumors of the anus and rectum are uncommon because these are tumors really of the anal canal. I am going to talk about the squamous, the basaloid, cloacogenic tumors of the anus. Basically anal canal tumors fall into this squamous, basaloid or cloacogenic category. Above the pectinate line there is a zone of transition here from an adenomatous epithelium of the rectum and the large bowel, down to a non-keratinizing squamous epithelium of the anal canal. Then out here in the perianal skin you have typical skin cancers, which would be keratinizing squamous carcinomas. There is a big difference, biologically, in the treatment orientation between a tumor that occurs here and a tumor that occurs there in the rectum proper. A rectal cancer drains to the internal hemorrhoidal nodes and the ileac nodes. The anal carcinomas drain to the superficial ileac nodes. If you look at the tumors that drain to the ileac nodes, aside from local skin cancers in the ileac area, you have – in females – you have labial cancer, which of course is a cancer of older … it tends to be a cancer of older females. You have anal canal cancers. You have penile cancers in men, which are quite an uncommon cancer in this country, and anal cancers are the main ones that will drain to the inguinal nodes and not drain internally.
If you look at the epidemiology of anal cancer you’ll see that it represents a relatively small percentage of the large bowel cancers. Of course, the anus is only about an inch, inch-and-a-quarter, long. If you look, there has been a difference in the occurrence of this tumor. For most of this century it was more common in people above the age of 55, it was about twice as common in women as men, was associated with people that had previous anal-rectal pathology; hemorrhoids, fissures, perhaps anal warts. And in the recent past it has increased significantly in men below the age of 45 and tends now to be more common in men. So there is really a bimodal peak. You still see the older patients but you do see younger patients. Why this occurred is of considerable interest and is telling us something about viral carcinogenesis, actually.