CA 15-3 elevations according to breast cancer subtypes at initial diagnosis of metastatic breast cancer (MBC).

e11109 Background: CA 15-3 is the most commonly used tumor marker for monitoring therapeutic effect in breast cancer and considerable portion of patients show increased CA 15-3 level at initial diagnosis of metastatic breast cancer (MBC). The tumor marker originated from the membrane epithelial mucin 1 gene (MUC1 gene), which is expressed at the luminal epithelial layer where hormone receptor (HR)-related genes are enriched. Because MUC1 is a luminal cell marker, we hypothesized that the elevation of CA 15-3 would be different according to breast cancer subtypes. Methods: A total of 536 patients with newly diagnosed MBC between 2000 and 2009 who had available clinical data including immuhistochemistry (IHC) for ER, PR, and HER2 were included. Patients were classified into three groups according to receptor status; ER and/or PR+ (Hormone Receptor, HR +), ER-/PR-/HER2+ (HER2 enriched), and ER-/PR-/HER2- (triple negative, TN) patients. Results: The median levels of CA 15-3 were 15, 22 and 37 for patients wit...