The Seed of Health
An alternative therapy following breast cancer surgery drastically reduces treatment time and concentrates radiation where it is most needed.
The MammoSite Radiation Therapy System brings the technology of brachytherapy to women who have undergone a lumpectomy—the removal of a tumor within the breast. Unlike traditional external radiation, in which high energy X-rays focus on the breast from 
outside the body, brachytherapy works from the inside out: Physicians temporarily insert a radioactive seed into the cavity left in the breast after the tumor was removed surgically.
The U.S. Food and Drug Administration approved MammoSite for treatment of invasive carcinoma in May 2002.
Instead of the five-to-seven weeks’ worth of daily office visits required for external radiation treatments, patients receiving MammoSite can complete radiation after only four or five days of therapy. That may be especially attractive to women who live far from their treatment center or who juggle daily responsibilities in their workplace or home.
And because physicians place the radiation source at the site of the patient’s tumor, the rays reach the very tissues surrounding the tumor where cancer is most likely to return.
“The benefit with MammoSite is that the source can enter the breast so quickly that you have minimal radiation to the rest of the breast,” says Oscar E. Streeter Jr., M.D., associate professor of radiation oncology at the Keck School of Medicine of USC. “We want to focus radiation only to the area most at risk: the local area around the tumor.”
Radiation therapy is meant to destroy any cancer cells that may remain after surgery. Studies have shown that small breast cancers treated through lumpectomy are most likely to recur near the original tumor.
This is how MammoSite works: After a patient recovers from her breast cancer surgery, a radiation oncologist threads a catheter through the skin until it reaches the cavity left by the tumor, usually about 2 or 3 centimeters wide. A balloon on the catheter’s tip inflates with liquid within the cavity, and a tiny bit of radioactive material is placed within the balloon. The patient then goes home.
Four or five days later, she returns to USC/Norris, where the radiation oncology team removes the catheter and radiation source, finishing her treatment. Because the radiation source is so tiny, there is no risk of radiation exposure to family members or friends at home during the therapy.
Gabor Jozsef, M.D., associate professor of radiation oncology, explains that when the seed is placed in the MammoSite balloon, the seed emits X-rays in all directions—much like light emanates from the sun.
The dose of radiation is most highly concentrated right at the edge of the tissue cavity, Jozsef explains, but declines further away from the radioactive seed. Within tissue that lies one centimeter away from the edge of the tissue cavity, for example, the dose of radiation already has shrunk by half—and it keeps getting lower and lower the further away the tissue is from the site of the former tumor.
Brachytherapy is already a household word in the world of prostate cancer, as many oncologists offer it as a radiation therapy option to men with that malignancy. (The word brachy means “a short distance” in Greek, and refers to the closeness between the radiation source and the tissue physicians aim to irradiate.)
But breast brachytherapy is rarer and has only been around since the early 1990s. Until now, the procedure has been complex and invasive. Physicians have had to insert between 14 and 25 catheters with seeds in the breast to provide enough radiation to the right tissue area. MammoSite, however, has reduced that to a single catheter.
Data back up brachy-therapy’s effectiveness. Two recent studies following 200 women for five years suggest that brachytherapy is as effective as external beam radiation in preventing breast cancer from coming back in women who have had a lumpectomy.
Deirdre Cohen, M.D., associate professor of radiation oncology, stressed that the therapy is appropriate only for certain cases of breast cancer.
“This is not for everyone,” Cohen says. “This is for patients with a small tumor, with a good margin around it. Ideally, you’re treating only those women with possible microspread of cancer to the immediate surrounding tissues.”
First of all, the treatment is meant to be a component of breast-conserving therapy, accompanying a lumpectomy. Lumpectomies generally are an option for women with early stage tumors (up to about 3 centimeters across) that have not spread. Because of mammograms and early detection methods, about seven out of 10 breast cancers today are considered treatable through lumpectomy.
Secondly, women with very small breasts may not be good MammoSite candidates, oncologists say. Tumors too close to the ribs or closer than 5 millimeters to the skin also make such treatment difficult.
Finally, older women tend to be better candidates than younger patients. “The younger you are when you get breast cancer, the more aggressive the cancer tends to be,” Cohen says. “This treatment would be best for nonaggressive tumors, so patient age and characteristics of the cancer play a part in making therapy decisions.”
Currently, the U.S. Food and Drug Administration has only approved MammoSite for the treatment of small, invasive breast cancers. But Streeter is hopeful that it will work against ductal carcinoma in situ, or DCIS, a condition in which cancerous cells are confined to the milk duct and have not spread to surrounding fatty tissue.
USC/Norris likely will lead testing on the effectiveness of MammoSite for DCIS, Streeter says.
Melvin J. Silverstein, M.D., professor of surgery and medical director of the Harold E. and Henrietta C. Lee Breast Center, says he strives to treat patients with DCIS without any radiation at all. A renowned DCIS expert, Silverstein always tries to remove a sufficiently large amount of tissue around the suspected DCIS area, then restores the look of the breast using oncoplastic techniques that combine plastic surgery and cancer surgery.
But if pathologists find that the area of clear, healthy tissue surrounding the excised tumor turned out to be too narrow, then radiation oncologists must irradiate the breast to destroy any potential remaining cancer cells—just as they do in women with invasive cancers. In that case, MammoSite would be an excellent alternative for DCIS patients, Silverstein says, if it proves effective in trials.
“The data on invasive cancers is quite favorable,” Silverstein says, “so we’re excited about it.”
For more information about the MammoSite Radiation Therapy System, or to learn more about The Doctors of USC, call 1-800-USC-CARE (1-800-872-2273).
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