Using Proliferative Markers and Oncotype Dx in Therapeutic Decision-Making for Breast Cancer: The B.C. Experience

Background: Proliferative scoring of breast tumours can guide treatment recommendations, particularly for estrogen receptor (ER)–positive, HER2-negative, T1–2, N0 disease. Our objectives were to (1) estimate the proportion of such patients for whom proliferative indices [mitotic count (MC), Ki-67 immunostain, and Oncotype DX (Genomic Health, Redwood City, CA, U.S.A.) recurrence score (RS)] were obtained; (2) compare the indices preferred by oncologists with the indices available to them; (3) correlate Nottingham grade (NG) and its subcomponents with Oncotype DX; (4) assess interobserver variation. Methods: All of the ER-positive, HER2-negative, T1–2, N0 breast cancers diagnosed from 2007 to 2011 (n = 5110) were linked to a dataset of all provincial breast cancers with a RS. A 5% random sample of the 5110 cancers was reviewed to estimate the proportion that had a MC, Ki-67 index, and RS. Correlation coefficients were calculated for the RS with NG subcomponent scores. Interobserver variation in histologic grading between outside and central review pathology reports was assessed using a weighted kappa test. Results: During 2007–2011, most cancers were histologically graded and assigned a MC; few had a Ki-67 index or RS. The NG and MC were significantly positively correlated with RS. The level of agreement in histologic scoring between outside and central pathology reports was good or very good. Very few cases with a low MC had a high RS (1.8%). Conclusions: Patients with low NG and MC scores are unlikely to have a high RS, and thus are less likely to benefit from chemotherapy. In the context of limited resources, that finding can guide clinicians about when a RS adds the most value.