Hello, Thanks for the query. I have gone through your short description and I can understand your concerns. As per your description it seems like an abscess(collection of pus under the skin). The other rare possibility is an infected axillary lymph node. A doctor can differentiate between the look in matter of seconds. The chances for a cancer is extremely unlikely. I suggest you to consult a general surgeon and get the following things done:- 1.The pus and debris has to be removed by a minor procedure called incision and drainage. in case of an infected lymph node it has to be surgically excised and sent for for biopsy to rule out any cancerous change. I m of the opinion that the possibility of cancer in very rare. 2.A short course of antibiotics is needed for five to seven days. 3.If you have pain you can use simple analgesics like ibuprofen or acetaminophen. 4.Check your blood sugar level to rule out diabetes. You don t need to worry regarding this because chances for a cancer is unlikely in this case. If you are really worried about cancer,Do frequent self breast examination to look for any palpable lumps. You can also go for mammography in every sixth month. Hope I have answered your query. Wishing you good health. Regards. Dr.Shinas Hussain