DL, my understanding is that fat necrosis occurs when the tissue isn't receiving sufficient blood or oxygen. Or in your case could be the radiation just somehow killed it, like it killed the cancer cells. If it's getting larger, sounds like it might be continuing to die. What does your surgeon say? Or oncologist? I believe the only thing you can do is remove it; it won't come back to life. Suggest you make a dr. appt. to find out what's up, rather than just let it slide. Good luck- PJH