Abstract
Oncotype DX is a gene expression profile used to guide chemotherapy decisions for early stage breast cancer. Invasive lobular carcinoma (ILC) is a histologic subtype with lower recurrence risk. In our predictive model, progesterone expression, Ki-67, estrogen expression, age and tumor size predicted recurrence risk in ILC. If validated, this model may provide an alternative to Oncotype DX testing in certain patients with ILC.
Introduction/Background: Oncotype DX (Genomic Health, Redwood City, CA) uses reverse transcriptase polymerase chain reaction analysis to measure tumor gene expression for determining recurrence risk (RR) and guiding chemotherapy decisions for breast cancer patients. Invasive lobular carcinoma (ILC) is a histologic subtype that has not been the focus of prior studies validating Oncotype DX. The study purpose was to develop a model using histologic tumor characteristics to predict uniformly low Oncotype DX Recurrence Scores (RS) in ILC. Patients and Methods: ILC cases in our pathology database with Oncotype DX testing were identified. Histologic tumor characteristics, immunohistochemical (IHC) of estrogen receptor (ER)/progesterone receptor (PgR) percent, HER2, E-cadherin expression, and Ki-67 levels were obtained for cases. Discriminant analysis was used to test the hypothesis that tumors classified as lower/higher risk based on Oncotype DX RS would differ significantly on a linear combination of variables. Results: From 2006 2014, 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 PgR% followed by Ki-67 provided the greatest contribution to discern low versus elevated RS. A subset of 57 cases (similar to 36%) with predicted probabilities > 86% for either low or high RS yielded 96.5% correct classification, 92.3% sensitivity, and 97.7% specificity. Conclusion: Our analytical model may be useful in predicting lower RR in patients with ILC. If validated, this provides a faster and less expensive alternative to Oncotype DX testing in certain patients with ILC. (C) 2016 Elsevier Inc. All rights reserved.
