THURSDAY, Sept. 4 (HealthDay News) -- Some women with early stage or locally advanced HER2-positive breast cancer may fail to respond to trastuzumab because their tumors have converted to HER2-negative status, according to research presented at the 2008 Breast Cancer Symposium, held Sept. 5 to 7 in Washington, D.C.
Elizabeth A. Mittendorf, M.D., of the University of Texas MD Anderson Cancer Center, and colleagues studied 143 patients whose tumors initially tested HER2-positive and were treated with a combination of chemotherapy and trastuzumab prior to surgery.
The researchers found that 72 (51.1 percent) achieved a pathologic complete response while 59 (41.8 percent) achieved a partial response, six (4.3 percent) had stable disease and four (2.8 percent) had progressive disease. After examining pre- and post-treatment tissue from 23 patients who did not have a pathologic complete response, they found that seven (30.4 percent) of the initially HER2-positive tumors had converted to HER2-negative status. After a median follow-up of 10.2 months, they also found that patients who did not achieve a pathologic complete response were significantly more likely than those who did to experience relapse.
"This phenomenon is important for providers to keep in mind so we can provide patients with the most appropriate targeted therapy for their cancer's biology," Mittendorf said in a statement. "We don't yet know on a molecular level what causes tumors to change. This is an area that deserves more research."
Abstract #150
