Anal cancer

Anal cancer, also called anal carcinoma, is uncommon. It starts in the anal canal, the passage that stool goes through on its way out of the body, or in the perianal skin, the skin around that opening. Doctors call it a malignant neoplasm, which is the technical way of saying cancer. The most common type is squamous cell carcinoma. Squamous cells are flat cells, stacked in layers like the scales on a fish, that line part of this area.

In squamous cell carcinoma, the main risk factor is the human papillomavirus, or HPV, when the body doesn't clear the infection and it hangs on for a long time. That's what doctors call a persistent infection. The virus gets into the basal cells, the ones in the deepest layer of the lining, right at the transition zone, the border where one kind of lining gives way to another. Once the virus is inside, the cell starts making viral proteins called E6 and E7. These are oncoproteins, meaning proteins that push the cell toward cancer.

And they push in more than one way. On one hand, they make the cell multiply faster. On the other, they break the cell's natural brakes, the tumor suppressor pathways that normally keep it from growing too much. Think of a car with the gas pedal floored and the brakes broken.

As for what people actually notice, the most common sign is bleeding from the rectum or anus. Next in line come pain in the anus and a palpable mass, which simply means a lump you can feel.