Ziggy,
Can't say I've been there exactly, but I had a large "mass" and fistula from the rectum up into a part of the small intestine. They cut and patched, rotorooted the infected blood veins, took out suspicious tissue (never did understand if it was cancerous or not, the guy was an ex-MASH doc, just did the work and moved on), and I ate soft foods and soaked in the bathtub everyday for weeks, and got over it, except for the fact that the rectum didn't quite close right. When briefs are on sale, I stock up :(
There is good news of a sort. You've had RT already. RT tore me a new one in the new damage to the scars from the prior surgery.
The surgery to the rectum is a true pain in the arse, but with a proper doughnut cushion and some ibuprofen, manageable.
I'll add my vote for hoping it is benign. At least they found it early.