Most of the time cancerous lumps do not hurt, but only a doctor can evaluate the lump to be sure. A mammogram and ultrasound can determine if it is a cyst. Cysts can be drained to relieve the pain. Draining is a simple procedure in the doctor's office. If it turns out to be a solid lump, a biopsy may need to be done to rule out cancer. The vast majority of lumps that are biopsied turn out not to be cancer. So the answer to your question "Is it cancer?" is probably not, but a doctor will need to check it out.
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