I developed some kind of lump near the top of one of my butt cheeks. It was quite a bit denser than the surrounding tissue and it pointed up in a way that it could have been used as a hook to hang a hat on, if for some reason I was naked and needed to carry an extra hat around.
My doctor didn't know what it was, and sent me to have a biopsy. The biopsy showed that it was not cancerous.
It was way too big for my doctor to consider removing, and he sent me to a surgeon to see if she could remove it in her office. She said it was too big for that, and it would need to be done in a hospital. She also had no idea what it was.
Next stop was a dermatologist to see if he had any ideas what it was and wht to do about it (short of surgery in the hospital). He too had no idea what it was. He checked with some colleagues at the University of Washington, describing it to them. They had no idea either, and wanted me to come over to let them look at it, and also show it to the medical students as an example of the strange ass (no pun intended) things that the human body sometimes does that they will encounter as doctors and have no idea what the heck is going on.
Since it wasn't cancerous, and, aside from dashing any hopes I might have had of quitting programming to become a nude butt model, didn't cause any problems I declined and just ignored it.
A few years later, it started shrinking, and a few months later was gone.
One of the doctors told me that this kind of thing--a patient with some weird thing that the doctor does not recognize--is a lot more common than most people realize.