I can not answer your question......but I have a question for you. April 22nd, I had an excisional biopsy on my breast, near my left armpit. The results came back good news. Fibryocystic disease. Now, I've found a lump in the center of my chest, on the hard flat part (and I am large chested.) I've been researching online......and it appears that is where the internal mammary lymph nodes are? Can they be felt? Does this sound similar to your mom's? Does she know it's an internal mammary lymph node?