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Please avoid meddling with the lump as you could introduce infection. What is your age. Do your mother, sisters have history of breast cancer
. Are there any lumps in your breasts. Any weight loss
. The armpit swelling could indicate enlarged lymph node
. It could be due to infection also as a cause. Not to panic. Go step by step. Consult a Surgeon and after thorough checkup and get an FNAC done. The results would indicate the possible pathology and the cause as well. Usually it is infections and would subside with antibiotic treatment but in your case we have to be cautious.