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Chemosensitivity and Stratification by a Five Monoclonal Antibody Immunohistochemistry Test in the NSABP B14 and B20 Trials

Authors' Affiliations: ¹ Applied Genomics, Inc., Burlingame, California; ² Division of Pathology and ³ Biostatistical Center, ⁴ National Surgical Adjuvant Breast and Bowel Project; ⁵ Department of Biostatistics, Graduate School of Public Health, University of Pittsburgh; ⁶ Allegheny General Hospital, Pittsburgh, Pennsylvania; and ⁷ Applied Genomics, Inc., Huntsville, Alabama

Requests for reprints: Douglas T. Ross, Applied Genomics, Inc., 863 Mitten Avenue, Suite 103, Burlingame, CA 94010. Phone: 650-697-8900; Fax: 256-533-1474; E-mail: dross{at}applied-genomics.com.

Purpose: To test the association between risk stratification and outcome in a prospectively designed, blinded retrospective study using tissue arrays of available paraffin blocks from the estrogen receptor–expressing, node-negative samples from the National Surgical Adjuvant Breast and Bowel Project B14 and B20 tamoxifen and chemotherapy trials.

Experimental Design: Tissue arrays were stained by immunohistochemistry targeting p53, NDRG1, SLC7A5, CEACAM5, and HTF9C. Risk stratification was done using predefined scoring rules, algorithm for combining scores, and cutoff points for low-risk, moderate-risk, and high-risk patient strata.

Results: In a univariate Cox model, this test was significantly associated with recurrence-free interval [HR, 1.3 (95% confidence interval, 1.1-1.6); P = 0.006]. In a multivariate model it contributed information independent of age, tumor size, and menopausal status (P = 0.007). The Kaplan-Meier estimates of the proportion of recurrence-free after 10 years were 73%, 86%, and 85% for the high-risk, moderate-risk, and low-risk groups (P = 0.001). The Kaplan-Meier estimates of the breast-cancer-specific-death rate were 23%, 10%, and 9% (P < 0.0001). Exploratory analysis in patients 60 years old showed Kaplan-Meier estimates of the proportion of recurrence-free of 78%, 89%, and 92%. Both high-risk and low-risk groups showed significant improvement on treatment with cytotoxic chemotherapy.

Conclusions: Immunohistochemistry using five monoclonal antibodies assigns breast cancer patients to a risk index that was significantly associated with clinical outcome among the estrogen receptor–expressing, node-negative tamoxifen-treated patients. It seems that the test may be able to identify patients who have greater absolute benefit from adjuvant chemotherapy compared with unstratified patient populations. Exploratory analysis suggests that this test will be most useful in clinical decision making for postmenopausal patients.