Utility of Oncotype DX risk assessment in patients with invasive lobular carcinoma (ILC).

Abstract

28 Background: Oncotype DX (Genomic Health, Redwood City, CA) is a breast cancer assay that uses reverse transcriptase polymerase chain reaction (RT-PCR) to measure gene expression in paraffin-embedded tumor tissue, which correlates with recurrence risk. This test is used to guide chemotherapy decisions in patients with estrogen receptor-positive breast cancer. Invasive lobular carcinoma (ILC) is a distinct histologic subtype, inherently estrogen receptor rich, that has not been the unique focus of prior studies validating Oncotype DX. The study purpose was to determine if there are certain features of ILC that predict uniformly low Oncotype DX Recurrence Scores (RS) such that Oncotype DX testing may be unnecessary, saving patients time and financial resources. Methods: A search was conducted of all ILC cases having Oncotype DX testing in our hospital pathology database. The Oncotype DX RS, histologic tumor characteristics (including subtype and grade), immunohistochemical (IHC) analyses of estrogen receptor (ER)/progesterone receptor (PR) percent (by image analysis), E-cadherin expression, and Ki-67 levels were obtained for each case. Discriminant analysis was used to test the hypothesis that tumors classified as low or high risk based on the Oncotype DX RS would differ significantly on a linear combination of selected variables. Results: From 2006 to 2013, 158 cases of ILC having Oncotype DX testing were identified; 90 low risk (RS <18), 66 intermediate risk (RS 18 – 30) and 2 high risk (RS > 30). Discriminant analysis showed that PR% followed by Ki-67 provided the greatest contribution to discriminating between low versus high RS. A subset of 57 cases (~ 36%) with predicted probabilities > 86% for either low or high RS yielded 96.5% correct classification, 92.3% sensitivity, and 97.7% specificity. Conclusions: Our analytical model may be useful in predicting high versus low recurrence risk in some patients with ILC. If validated, this provides a faster and less expensive alternative to Oncotype DX testing in certain patients with ILC.