Researchers have validated a new method of tissue analysis, called tissue microarrays, to determine the ‘intrinsic subtype’ of a breast tumor and to predict whether a patient with breast cancer that has spread to the lymph nodes will benefit from adjuvant paclitaxel (Taxol) chemotherapy.Use of breast cancer subtyping to predict response to a specific anticancer drug will improve physicians? ability to personalize treatment to maximize benefits and spare patients from unnecessary side effects.?Breast cancer is an incredibly complicated, challenging disease, and the more we learn about how to customize treatment based on individual tumor biology, the more we will be able to improve outcomes for patients,? said lead author Torsten Nielsen, MD, PhD, associate professor of Pathology & Laboratory Medicine at the University of British Columbia in Vancouver. ?In this study we validated a new and highly efficient tissue assessment technique ? tissue microarrays ? that determines the molecular features of a tumor, or its intrinsic subtype, and predicts whether a patient will benefit from paclitaxel chemotherapy.?Tissue microarrays are antibody assays that can be used to detect molecular markers in tissue samples as small as 0.6 mm across and 0.004 mm thick. In this study, researchers used the antibody assays to identify the breast cancer intrinsic subtypes ? such as the HER2-positive and basal subtypes ? which are associated with response to paclitaxel.Researchers in this study used tissue microarrays to perform intrinsic subtyping on breast cancer tissue obtained from 2,039 of the 3121 women who participated in the Cancer and Leukemia Group B study 9344 (CALGB 9344) whose outcomes were representative of the trial as a whole. In the 1990s, this study showed that adding adjuvant paclitaxel to therapy with doxorubicin and cyclophosphamide was associated with a 5% absolute improvement in disease-free survival, though not all patients experienced this benefit. Among the 42% of subjects with complete ER and HER2 information, no benefit was found in the ER+/HER2- subset.Researchers in the current study compared the tissue microarray findings with data on the patients? clinical outcome. They showed that women with the intrinsic subtype Luminal A did not benefit from adding paclitaxel to their treatment. However, women with aggressive intrinsic subtypes, such as HER2-positive breast cancer or basal breast cancer, did derive significant benefit from adjuvant paclitaxel.If confirmed by future clinical research, the biological subtyping methods developed using tissue microarrays will add to the information gained by existing biological tests (such as those for hormone receptors and HER2) to determine the optimal treatment for women diagnosed with breast cancer. The technique could also play a significant role in analyzing tissue samples from other large clinical trials.The results of this studies were presented duiring the 2009 (third) Breast Cancer Symposium held from October 8-10, 2009, at the San Francisco Marriott.Reference: T. O. Nielsen, S. D. Jewell, A. D. Thor, D. Gao, C. M. Perou, G. Broadwater, L. N. Harris, D. F. Hayes, D. A. Berry, M. J. Ellis, on behalf of the Cancer and Leukemia Group B. Intrinsic subtype and response to paclitaxel in CALGB 9344 tissue microarrays Presented on Thursday, October 8, 2009 at the American Society of Clinical Oncology (ASCO) 2009 Breast Cancer Symposium.