Gene profiling identifies breast cancer subtypes

AORN Journal, Sept, 2007

Researchers using gene chips to profile breast cancer tumors have identified markers for tumor subtypes that are resistant to trastuzumab, the primary treatment for human epidura[ growth factor receptor-2 (HER2)-positive breast cancer, according to a February 20, 2007, news release from the American Association for Cancer Research. Early identification of HER2-positive tumors that are resistant to trastuzumab could help physicians refine treatment for the 25% to 30% of patients with this type of breast cancer tumor.

Researchers studied 48 patients with newly diagnosed and operable stage II or stage III breast cancer. Biopsies were taken before the patients were treated for 12 weeks with a combination of trastuzumab and vinorelbine, a chemotherapy medication used for patients with lung cancer. After treatment, the tumors were surgically removed and studied. For both the baseline and post-therapy samples, gene chips were examined for RNA that had been activated to produce proteins.

The researchers found that HER2-positive tumors that did not respond to trastuzumab were more likely to express insulin-growth factor receptor 1 (IGF-1R) and to overexpress the HER2 growth factor protein. In addition, these tumors were more likely to express genes associated with basal-like breast cancer and to express a variety of growth factors. Tumors that expressed IGF-1R had a treatment response rate of less than half that of tumors that did not express this growth factor receptor.

If future studies validate these findings, researchers hope gene profiling can be used to identify patients who would be less responsive to trastuzumab before treatment begins. Physicians would then be able to tailor their therapy accordingly.

Gene Profiling Predicts Resistance to Breast Cancer Drug Herceptin [news release]. Philadelphia, PA: American Association for Cancer Research; February 20, 2007.