<s>[INST] My friend is a 25 year old male who developed what loojed luke a cyst under his armpit a littlr over a month ago. Since then the center of his armpit has become a huge hard lump. Probably about 2 inches long and 1 inch wide. Meanwhile the cyst type thing has continued to grow and finally came to a pus filled head two days ago. A little greenish white pus came out but appears to have become larger, redder, inverted and he says the pain is much worse now. We are trying to figure out what is going on , thank you. [/INST] HiWelcome to hcmYour friend must be having sebaseous cyst which has got infected now. He need to see a surgeon to drain it out. This can also be a lymph node enlarged either due to infection or tuberculosis. Any case treatment is drainage of pus and send the pus for culture sensitivity to know exact cause and further treatment accordingly.Regards. </s>