15 Year Old Diagnosed With Aplastic Anemia. Undergone Bone Marrow Transplant. Lump Under The Nipple Growing In Size, Rashes On The Feet. Advice?

Hi, My son is a 15 year old who was diagnosed with severe aplastic anemia 2 years ago. He under went a bone marrow transplant on January 12 2011, his younger brother was a 10/10 match. Recenetly he has developed a lump under his nipple that has doubled in size over the past three weeks. The lump is fairly painful for him. He has also developed a faint petechiae rash on the tops of his feet. We had an ultrasound done week one after we noticed the lump, but the shadowing of the nipple prevented a clear picture from being seen. After week three, and the increase in size, he had another ultrasound done. We were told that it was likely breast tissue , but they would biopsy it anyhow. Should I be concerned, and if it is likely breast tissue why put his body through more?