Hello, Welcome and thanks for posting your query to HCM. You have not mentioned the details regrading your problem. We need certain important things related to your problem such as your age, time since you noticed it, size or shape of lump, is it movable or fixed and skin over the lump. There can be multiple possibilities from your short history such as growth of fatty tissue to due to blockage of oil gland or simple lymph node also. It is better to consult either a dermatologist or a surgeon if you perceive enlargement or more pain in the lump. You can also consult for you other symptoms of pain over the chest and armpits. Mean while do not try to pinch, pop or squeeze the lump. Hope it helps. with good health wishes, Dr Sanjay K Kanodia MD ( Dermatology)