The lump could be from the radiation. My nurse at the radiation center told me this is a side effect of radiation. One of the side effects besides burning etc. . I believe she called it radiation fibrosis . She said it usually shows up a month afterwards. But can not show up till a year down the road. But usually not longer than that. She was just trying to say, if I feel something funny, don’t freak out and get scared, but do let them know.