When a suspicious abnormality is detected on a screening mammogram and no lump is felt, a biopsy is typically recommended to determine the cause.  Currently, needle biopsy rather than an open surgical biopsy is most commonly performed to make the diagnosis.  The use of core needles with vacuum assistance allows the area to be sampled by extracting small tissue cores through the needle in a quick and relatively painless manner.  When the abnormality is visible only on mammography and not on ultrasound the radiologist uses mammography to guide the biopsy with specialized equipment known as stereotaxis. 

There are two basic types of stereotactic machines.  With the first, the prone table, the patient lies on her abdomen with the breast suspended through an opening in the table and the biopsy team is seated under the table taking the samples.  With the upright stereotactic machine the patient either lies on her side or sits up for the biopsy.  In both cases the equipment allows for very precise targeting and sampling of the abnormality.  Typically 4 to 12 small samples are obtained from the abnormality in order to have enough material for the pathologist to make an accurate diagnosis.  The needle is inserted through a small nick in the skin so no stitches are necessary to close the site.

After the procedure the patient will have a bandage and will place ice over the area to minimize bruising and tenderness.  The tissue is sent to a pathologist who will study it to determine the diagnosis.  Based on the diagnosis and the findings on mammography the radiologist will recommend either follow-up mammography in 6 or 12 months or surgery.  Surgery is performed when the needle biopsy shows cancer or a higher risk lesion or pre-cancer.  In the case of the high risk lesion, the biopsy may or may not have removed all the abnormal cells, so an excision of a small area of tissue around the biopsy site is needed to remove any additional cells.

In most facilities, for all patients in whom stereotactic biopsy is recommended and performed, about 20% to 40% actually show cancer and the remainder are benign.  This technique is one of the great advances in breast imaging in that it allows women to have an accurate diagnosis of a breast abnormality in a minimally invasive way.  Unnecessary surgery is avoided for benign lesions and the best surgical procedure is performed when a diagnosis of cancer is made through a needle biopsy.

By Ellen Shaw de Paredes, MD, FACR