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Prognostic Effect of Basal-Like Breast Cancers Is Time Dependent: Evidence from Tissue Microarray Studies on a Lymph Node–Negative Cohort

Authors' Affiliations: ¹ Department of Laboratory Medicine, St. Michael's Hospital; ² Laboratory Medicine and Pathobiology, ³ Public Health Sciences, and ⁴ Department of Medical Genetics and Microbiology, University of Toronto; and ⁵ Samuel Lunenfeld Research Institute and ⁶ Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, Toronto, Ontario, Canada

Requests for reprints: Frances P. O'Malley, Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario, Canada M5G 1X5. Phone: 416-586-4548; Fax: 416-586-8628; E-mail: fomalley{at}mtsinai.on.ca.

Purpose: To determine whether data obtained from tissue microarrays (TMA) of a prospectively accrued node-negative breast cancer cohort are prognostically informative, we compared data derived from TMA with previously determined molecular markers. Subsequent to this validation, we examined outcome in specific subgroups defined using TMA data.

Experimental Design: A consecutive series of 1,561 patients were followed for recurrence (median follow-up of 107 months). Estrogen receptor, progesterone receptor, p53, and HER2 expression, examined using TMA constructed from 887 tumors, was compared with status evaluated previously by biochemical and molecular methods. The associations with risk of recurrence were examined for biomarkers as well as for HER2, luminal, and basal subgroups defined by immunohistochemical expression.

Results: In line with earlier molecular studies, a significant risk of recurrence was found in patients with HER2 overexpression (relative risk = 2.30; P = 0.002) and p53-positive tumors (relative risk = 1.81; P = 0.005) in univariate Cox model analysis. Although complete concordance between methodologies was not observed for estrogen receptor and progesterone receptor, their associations with disease-free survival were consistent with established prognostic findings. Patients with basal-type tumors fared worse within 36 months of diagnosis but not thereafter.

Conclusions: This study shows the clinical validity of TMA in evaluating the importance of prognostic markers in this cohort. Furthermore, it shows a marked time-dependent effect in tumor subgroups, most notable within the basal subgroup. Our data suggest that patients with basal-like tumors may be broadly separable into two clinically distinctive groups: those likely to experience disease recurrence in the short term and those that will experience long-term survival.

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