Many lumps turn out to be cystsharmless sacs of fluid. "Almost all [cysts] are benign," notes Peter M. Jokich, MD, director of the Rush Breast Imaging Center at Rush University Medical Center in Chicago. But to know for sure, you may be sent for an ultrasound to see if the radiologist can get more information than a mammogram can show.
Also called sonograms, ultrasounds are great for spotting whether a lump is solid or fluid. They are not as good, however, as mammograms at identifying microcalcificationstiny calcium deposits that can indicate cancer when clustered together.
If your lump is solid, there's a chance it could be cancer, and you're on to the next test, which may be an MRI or a biopsy.