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Gynecomastia can usually be diagnosed from a physical exam and medical history. In most cases, tests are not necessary. But if the breast lump is unusually large, one-sided, tender, or hard and fixed, a biopsy may be done to rule out other problems.
Any man who finds a one-sided breast lump should let his doctor know if he has close relatives who have had breast cancer (mother, sister, or daughter). If there is any concern about cancer, a lump can be checked with a biopsy or surgery.