Hard to say if it is cancer in my case. It seemed to start with something like an insect bite that went wrong or my hitting a branch with my head when moving my big weedwhacker machine around under apple trees. But the guy who saw it took one look at it, asked no questions at all and just said "cancer". He's quite old and experienced I think. It does look a bit like some of the pics I have seen. Anyway I am not going to be arguing, I'll just get it done. It is pretty small, about 6 or 7 mm across.