My husband went for his first colonoscopy 7 years ago (age 50) and the doctor who was performing the procedures snagged something that she thought looked abnormal. He was diagnosed with anal cancer. He went through radiation and chemo for 2 months (getting radiated twice a week right under his balls, poor guy) and 3 months later was pronounced cancer free. As the months and years went by he began to notice that some of the skin on his shaft was starting to cover the head of his penis. He was cut at birth. He spoke to his doctor about it and the response we got was that while it's not common, there are times that as the body starts its healing process from receiving so much radiation, cells can kick into overdrive. He thinks that my husband had a burst of epithelial skin growth. So when he's flaccid it looks like he has a foreskin but everything goes back to normal when he is erect. He's not upset about it and I think it looks pretty cool.
