Implications of different CA 15-3 levels according to breast cancer subtype at initial diagnosis of recurrent or metastatic breast cancer.
ABSTRACT CA 15-3 is derived from proteolytic shedding of the extracellular domain of mucin 1 (MUC1) glycoprotein. Luminal subtype breast cancer shows a higher expression in MUC1 genes, and a positive relationship between MUC1 expression and estrogen receptor (ER) expression has been reported. In this study, we attempted to determine the difference of CA 15-3 level according to the subtype of breast cancer.
From January 2000 to December 2009, a total of 707 patients who were diagnosed with metastatic or recurrent breast cancer at Samsung Medical Center were included in this study. Among these, 536 patients with available clinical data including pretreatment CA 15-3 and immunohistochemistry for ER, progesterone receptor (PgR) and hormone receptor 2 (HER2) were analyzed in this study. Patients were classified into 3 groups according to their receptor status: ER-positive (ER+) and/or PgR+ irrespective of HER2 (HR+), ER-/PgR-/HER2+ (HER2-enriched) and ER-/PgR-/HER2- (triple negative, TN).
The supranormal values of CA 15-3 were frequently observed in HR+ breast cancer compared to other types (45.6% for HR+, 24.4% for HER2-enriched and 28.8% for TN; p < 0.001). The increase of marker levels differed significantly among the 3 groups (24 U/ml for HR+, 13 U/ml for HER2-enriched and 18 U/ml for TN; p < 0.001).
The increase of both marker levels and the frequency of supranormal values of CA 15-3 were more frequently observed in HR+ breast cancer, which is positively associated with MUC1 expression. These results could potentially serve as a basis for expanding the clinical implications of CA 15-3 in the field of clinical trials for novel targeted therapies in breast cancer.