Innovative use of somatostatin receptor scintigraphy (SRS), a nuclear medicine imaging technique looking at how the body functions at the molecular level, may provide near immediate selection of breast cancer patients for endocrine therapy and offers a new tool in fighting the disease, according to a study published in the Journal of Nuclear Medicine.

Advanced or metastatic breast cancer patients receive either hormonal or chemotherapy treatment, depending on the hormone sensitivity of a woman's tumor. In some women, the female hormone estrogen promotes the growth of breast cancer cells. Endocrine or hormonal therapy removes the influence of estrogen on breast cancer cells, preventing the cancer cells from growing and spreading.

"Our technique allows a fast and accurate selection of breast cancer patients for hormonal treatment," explained Bieke Van Den Bossche, M.D., Ph.D., nuclear medicine department, Ghent University Hospital, Ghent, Belgium. "In routine practice, patients are assigned to hormonal treatment—or not—depending on the hormone receptor status of the primary tumor," said Van Den Bossche, a co-author of the study. She added, "With conventional imaging techniques, it takes at least three to six months to evaluate if the disease is regressing, stabilizing or progressing. Obviously, every day that a patient goes without efficient therapy is a day too many."

Hormonal treatment provides good results with minor side effects, but only patients who have tumors and metastases (spread) sensitive to hormones benefit from this type of treatment, she said. "Because only about one-third of breast cancer patients initially respond to endocrine therapy, there is a need for patient selection," said Van Den Bossche.

"The only technique used now to determine whether a patient's tumor is sensitive to hormonal therapy is examination of a piece of tumor tissue in a lab to see if hormone receptors are present," said Van Den Bossche, adding that this method has low accuracy. "With our technique, it is possible to take an imaging scan of the entire patient—and treatment should be started when metastasis occurs—to evaluate if the tumor lesions are hormone sensitive and to assess what treatment would be efficient," she noted. "Our technique can assess hormone sensitivity with a whole-body imaging scan, which can be applied whenever needed in the course of the disease for all lesions at one time," she added.

While SRS is routinely used in nuclear medicine for diagnosis, Belgian and Italian researchers used SRS for therapy prediction—a new and promising field, noted Van Den Bossche. "We demonstrated the relationship between the expression of somatostatin receptors and the hormone sensitivity of human breast tumors along with use of somatostatin receptor imaging for selection of patients likely to respond to hormonal treatment," she said. By using 99mTc-labeled depreotide, which binds to somatostatin receptors and sends out flashes of light detected by a gamma camera, researchers were able to create an image of the presence of hormone-sensitive lesions in a patient's body. The study notes, "Sequential 99mTc-depreotide scintigraphy could allow for separation of responders and nonresponders immediately or as early as three weeks after initiation of treatment."

While these results come from an initial group of 20 patients, the team will continue to confirm the findings on a larger group of breast cancer patients, said Van Den Bossche. "This is necessary before a therapeutical consequence can be given to the SRS scan results. If the results are going to be in the same line, we could predict therapy response with an accuracy of 100 percent immediately or within three weeks after treatment initiation," she said.

SOURCES:
Journal of Nuclear Medicine, January 2006
Society of Nuclear Medicine (http://www.snm.org)