A biopsy is the most certain way to determine whether a breast lump is cancerous. Biopsies may be taken through a needle or through a minor surgical procedure. The results can also determine the type of breast cancer that is present in many cases (there are several different types of breast cancer). Treatments are tailored to the specific type of breast cancer that is present.
For example, a biopsy can tell whether the breast cancer has receptors for estrogen (ER-positive) and//or progesterone (PR-positive). This means the tumors grow in response to these hormones. About two-thirds of breast cancers are hormone receptor-positive. Medications can be given that act to help prevent growth of the tumor from stimulation by these hormones.