Clinical Validation of a Customized Multiple Signature Microarray for Breast Cancer

Purpose: Current histopathologic systems for classifying breast tumors require evaluation of multiple variables and are often associated with significant interobserver variability. Recent studies suggest that gene expression profiles may represent a promising alternative for clinical cancer classification. Here, we investigated the use of a customized microarray as a potential tool for clinical practice. Experimental Design: We fabricated custom 188-gene microarrays containing expression signatures for three breast cancer molecular subtypes [luminal/estrogen receptor (ER) positive, human epidermal growth factor receptor 2 (HER2), and “basaloid”], the Nottingham prognostic index (NPI-ES), and low histologic grade (TuM1). The reliability of these multiple-signature arrays (MSA) was tested in a prospective cohort of 165 patients with primary breast cancer. Results: The MSA-ER signature exhibited a high concordance of 90% with ER immunohistochemistry reported on diagnosis ( P P in situ hybridization (FISH; ratio ≥2.2; P P = 0.001), and luminal/ER+ TuM1-expressing tumors were significantly correlated with low histologic grade ( P = 0.002) and improved survival outcome in an interim analysis (hazard ratio, 0.2; P = 0.019). Conclusion: The consistency of the MSA platform in an independent patient population suggests that custom microarrays could potentially function as an adjunct to standard immunohistochemistry and FISH in clinical practice.