printable versionMRI could help to bolster detection of some cases of early stage breast cancer
Kathleen Horst
Frederick M. Dirbas
Early stage breast cancer could be more effectively detected, at least in some cases, by using magnetic resonance imaging in addition to mammography to help discover the full extent of the cancer—information that's crucial in deciding how best to treat a patient, according to early results from a study at the School of Medicine.
In the process of evaluating 51 patients for a study of partial-breast irradiation treatment, the researchers used MRI to help assess the extent of cancer within each patient's breast. In almost 10 percent of the patients, the MRI revealed more extensive cancer than mammography had shown.
Partial-breast irradiation is a relatively new approach to breast-conservation therapy. The standard treatment for women whose breast cancer is diagnosed at an early stage is a lumpectomy (surgical removal of the tumor along with a surrounding margin of healthy tissue) followed by radiation treatment of the entire breast. But whole-breast irradiation takes weeks, causes fatigue and skin irritation that linger for months, and may not always be necessary.
"In certain patients we may be over-treating by irradiating the whole breast," said Kathleen Horst MD, instructor in radiation oncology, who presented early results from the study Oct. 17 in Denver at the annual meeting of the American Society for Therapeutic Radiology and Oncology.
Because most tumors that recur do so in the location of the original tumor, some researchers are investigating whether radiation of the surgical cavity after a lumpectomy, along with a margin of surrounding healthy tissue, will achieve the same level of results as whole-breast irradiation.
The Stanford team is looking at two techniques of delivering accelerated partial-breast radiation. One approach delivers a single dose during the surgery, while the other approach involves two doses of radiation per day for five days after the operation. Because both methods deliver less total radiation than the whole-breast technique, the doses can be higher and still be safe. Either partial-breast approach could greatly reduce the side effects of radiation therapy, thus speeding the recovery process and also lowering the cost of treatment.
But there's a caveat.
If radiation is limited to only part of the breast, any microscopic cancer cells elsewhere in the breast that weren't detected by a mammogram would go untreated. This is where whole-breast irradiation has an advantage. If any spots of cancer have begun to form in areas away from the tumor, those areas get irradiated along with the rest of the breast, potentially knocking out small cancers before they can flourish.
That's why the researchers are using MRI, which can detect some cancers too small to be seen on a mammogram, to help make sure women considering partial-breast irradiation don't have any hidden cancers. In five of the 51 women in the study, MRI revealed just such cancer. Had these women been treated with partial-breast irradiation, cancerous cells outside the treatment area might have grown into tumors that may have necessitated a mastectomy.
"Ideally, we want to determine the full extent of breast tumors prior to surgery and radiation. Identification of larger tumors, or satellite nodules, can alter our surgical approach or suggest that partial-breast irradiation is not optimal for the patient," said Frederick Dirbas, MD, assistant professor in general surgery and principal investigator on the study. Out of the five women with additional cancer, two had lumpectomies followed by whole-breast irradiation and the other three had mastectomies.
But MRI isn't perfect. In addition to the five women whose treatment was radically altered by the MRI findings, there were five for whom the MRI detected suspicious spots that turned out not to be cancerous. Such false positives, combined with the several thousand dollars it costs to do MRI, has some researchers questioning the practicality of using MRI and partial-breast irradiation. Furthermore, while MRI may be highly sensitive, it still can miss some cancers.
Dirbas and Horst agree that partial-breast irradiation isn't appropriate for all early stage breast cancer patients. And Dirbas said he would like to reduce the number of false positives MRI can generate, but added that "we have had enough patients who have had unsuspected disease elsewhere in the breast that for now, on balance, we think the MRI is a useful adjunct to mammography."
As for the expense, the standard approach has its own cost issues. Some lumpectomy patients who haven't undergone MRI have larger cancers than anticipated, which are only discovered after surgery when the final pathology results are available. They then have to undergo another surgery to remove the additional tumors. "There is certainly a cost to these incremental procedures that the MRI can help avoid," said Dirbas.
As the clinical trial continues, Dirbas said the team will use MRI to help select patients who meet the guidelines for partial-breast irradiation because it appears to offer the greatest possibility of finding hidden cancers.
Other Stanford researchers contributing to the study are Debra Ikeda, MD, associate professor of radiology and director of breast imaging; Bruce Daniel, MD, associate professor of radiology; Don Goffinet, MD, emeritus professor of radiation oncology and otolaryngology; Sunita Pal, MD, clinical instructor of radiology, and Kent Nowels, MD, associate professor of pathology.
The study is funded by the Vadasz Foundation and the Northern California Chinese Unit of the American Cancer Society.