Use of clinical and treatment factors to predict survival outcome in nonmetastatic metaplastic breast cancer.

Abstract

11 Background: Although metaplastic breast cancer (MBC) represents < 1% of breast cancer, stem cell research has stimulated interest in the genetics and biology of MBC. Because prognostic clinical and treatment factors remain ill-defined for this rare breast cancer subtype, we queried a public cancer data registry to identify factors predictive of overall survival (OS) in MBC. Methods: Patients diagnosed with breast cancer from 2001-2008 were identified using the Surveillance, Epidemiology, and End Results (SEER) database. We included only patients with infiltrating ductal carcinoma (IDC) and MBC who had non-metastatic disease. Patients were evaluated by standard demographic, clinicopathologic, and treatment factors including age, race/ethnicity, extent of disease, tumor marker expression and treatment received. Differences between IDC and MBC were assessed using Chi-Square methods. OS across groups was measured using the Kaplan-Meier method and compared using the log-rank test. Cox proportional hazard and stepwise models were used to identify prognostic variables and to adjust for covariates. Median follow-up was 31 months. Results: Of the total 508,071 breast cancer cases, there were 1,246 (0.25%) patients with MBC and 392,809 (77%) with IDC. 5-yr OS for locoregional MBC and IDC was 67% and 84%, respectively (p<0.0001). When compared with IDC, MBC patients were older, had larger ER/PR negative cancers, and were more likely to have nodal disease. Factors predictive of worse OS in MBC on multivariate analysis are listed below. Tumor grade, ER/PR expression, and type of surgery (partial v. total mastectomy) did not impact OS. Of the treatment factors, only radiation affected OS (p=0.0002). Conclusions: To our knowledge this is the largest report of clinical and treatment factors predictive of outcomes in patients with MBC. Studies integrating clinical factors with molecular data may advance therapy that is more specific for this rare breast cancer subtype. [Table: see text]