A microcalcification is a buildup of calcium in one spot. They are common and most women will have a few on their mammogram at some point in time. Most of them are benign. Most women do worry about them, though - perhaps because they haven't been given a full explanation of what they are.
When should you worry? First, don't panic if you have microcalcifications because most women DO have them at some point. The doctor will take a look to see if they warrant further investigation.
This usually occurs when the microcalcifications are new, clustered tightly together, and appear when magnified to have irregular shapes. Rather than spherical, they look like grains of salt with irregular edges. This can be an early sign of breast cancer, most often non-invasive ductal carcinoma in situ (DCIS or stage 0 breast cancer).
Microcalcifications cannot be felt on clinical exam or your own breast self-exam. They do not hurt. This is the value of mammography - it finds them long before they can progress into an actual lump.
Most of the time, suspicious microcalcifications will be biopsied using a stereotactic technique that enables the doctor to pinpoint their location and remove a sample so it can be examined by a pathologist. The purpose of removing tissue using this technique is not to remove all of the microcalcifications but to get a representative sampling so a diagnosis can be made.
The specimens removed will resemble 1-inch spaghetti strips. These strips are X-rayed before being sent to pathology to ensure they contain the tiny "salt grains" that looked questionable. The doctor will also place a clip at the spot(s) in the breast where the samples were obtained. These clips will be important as markers for future mammograms and, if recommended, for surgery.
This type of biopsy technique requires only local anesthetic and requires no incision. It also prevents scarring of the inside of the breast. When there is scarring inside the breast from previous surgery like an open excisional biopsy, the mammogram shows this as an abnormality which warrants further investigation to ensure that it is just scar tissue and nothing more serious.
Did you know . . . the area of the breast most commonly forgotten by women during breast self-exams is underneath the nipple and areola.