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The Federal Drug Administration recently cleared a new medical device called a MammoSite Radiation Therapy System for patients with early stage breast cancer who have had a lumpectomy.

Breast cancer is a common malignancy among women in the United States with almost 200,000 new cases diagnosed each year. Breast cancer develops from cells in the breast and is defined according to various stages of progression. Patients diagnosed with stage I invasive breast cancer have a single location of cancer less than 2 cm (3/4 inch) in size that has not spread to the axillary (armpit) lymph nodes or sites distant from the breast. Patients diagnosed with stage II breast cancer have a primary cancer that either involves axillary lymph nodes and is less than 5cm (2 inches) in size, or is greater than 2 centimeters (3/4 inch) in size and does not involve any axillary lymph nodes. Stage I and II breast cancers are commonly referred to as early breast cancer.

Standard treatment of early stage breast cancer consists of a lumpectomy followed by radiation therapy. A lumpectomy, also known as conservation surgery, is surgery that removes only the cancer and surrounding tissue, leaving the majority of the breast intact. The purpose of a lumpectomy is to limit the amount of breast tissue removed, thereby reducing the disfigurement associated with removal of the entire breast. Following a lumpectomy, the most common location of a cancer recurrence is in the breast tissue in the vicinity of the primary cancer (local recurrence). Therefore, radiation therapy is used following a lumpectomy to kill cancer cells that may not have been removed during surgery, thereby reducing chances of a cancer recurrence.

Standard radiation therapy following a lumpectomy consists of a limited dose of radiation (50 Gy) to the entire affected breast. While this treatment leads to long-term outcomes similar to a mastectomy (complete removal of the breast), women under 50 years of age experience higher rates of local recurrences following this treatment regimen compared to their elder counterparts.

Brachytherapy Internal radiation is known by a number of names: “interstitial brachytherapy,” “seeds,” or “implantation.” These terms refer to treatment in which radioactive material is placed directly into or near the cancer. Because implant radiation focuses the radiation closely around the cancer, this form of radiation typically works best in patients with early stage cancers.

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MammoSite Radiation Therapy System, a hollow catheter with an inflatable balloon attached, is a form of brachytherapy. By implanting the device at the lumpectomy site and inflating the balloon through the catheter with the radiation, the radiation can be focused on the local area of the breast where recurrence is most likely and minimize radiation to the rest of the breast. Typically, a series of treatments are required over several days. Upon completion, the catheter and balloon are removed.

The FDA made its decision to clear the MammoSite device based on evidence from 25 patients who had undergone a lumpectomy followed by brachytherapy with the MammoSite device. This evidence suggested that compared to other brachytherapy devices, the Mammosite device was comparably safe and effective. The FDA has required that a warning be included with the MammoSite device that states that its safety and efficacy have not been compared to whole breast irradiation.

Patients with early stage breast cancer may wish to speak with their physician about the risks and benefits of treatment with the MammoSite Radiation Therapy System or participation in a clinical trial further evaluating the MammoSite Radiation Therapy System. This device does not replace whole breast irradiation. Future trials may determine the safety and efficacy of the MammoSite Radiation Therapy System compared to whole breast irradiation to treat breast cancer.

Reference: U.S. Food and Drug Administration. FDA Talk Paper. Available at: Accessed May 7, 2002.

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