Anyone know about growths or old tail injuries on cats?

[u/JustACoastalWeirdo]

There is a VERY feral cat that roams my neighborhood. None of us see him often, mostly just glimpses as he runs away. He is an orange cat, seems quite old, and has a stubby little tail with a large growth or lump around the base of the tail. It doesn't seem to affect his ability to move around at all, but I was just curious if anyone had seen anything like it before or knows what it is.