Penile cancer

Penile cancer is a malignant tumor: a growth of cells that can invade the tissues around it. It's uncommon, and it's almost always the same type. More than 95% of cases are squamous cell carcinoma, which starts in the flat cells that make up the outermost layer of the skin.

It usually starts on the glans, the head of the penis, or on the foreskin, the skin that covers it. At first it's something small that doesn't hurt: a nodule, which is a small round bump; a lump; or an ulcer, which is an open sore. Then it grows slowly outward across the surface, and it often covers the whole glans or the whole foreskin before it pushes inward into the corpora cavernosa, part of the tissue inside the penis, and into the shaft, the long part of the penis. Think of a water stain that spreads across the paint on a wall before it soaks into the wall itself.

We also know what tips the odds toward this cancer. Its strongest risk factors, the things that raise the chance of it showing up more than anything else, are high-risk types of human papillomavirus, or HPV, the types most closely tied to cancer; phimosis, when the foreskin is so tight that it can't be pulled back to uncover the glans; and smoking. Putting names to them helps make sense of where this cancer can come from.