Question: I developed a pea-sized lump in my right armpit on Thursday. It feels deep under the skin, is hard, fixed, and tender. The skin over it is intact with no redness, pus, or drainage, and the swelling has remained about the same size. I started my period today and I usually get mild breast tenderness before my periods, but this is the first time I’ve had an armpit lump. I shaved my armpit about two weeks ago. I have started applying mupirocin ointment and warm compresses. Could this be an inflamed hair follicle, boil, cyst, reactive lymph node, or something related to hormonal changes? Does this presentation raise concern for breast cancer, or is that less likely given the sudden onset and tenderness?