Effect of tumor size on breast cancer-specific survival stratified by joint hormone receptor status in a SEER population-based study.

Background & Aims: The prognostic value of tumor size is variable. We aimed to characterize the interaction between tumor size and hormone receptor (HoR) status to determine breast cancer-specific mortality (BCSM).
Methods: We used the Surveillance, Epidemiology and End Results (SEER) registry to identify 328, 870 female patients diagnosed with invasive breast cancer from 1990 through 2010. Primary study variables included tumor size, joint HoR status and their corresponding relationship. Kaplan-Meier and adjusted Cox proportional hazards models with interaction terms were utilized.
Results: The multivariable analysis revealed a significant interaction between tumor size and HoR status (P < 0.001). Using tumors 61-70 mm in size as the reference for estrogen receptor-negative (ER-) and progesterone receptor-negative (PR-) disease, the hazard ratio (HR) for BCSM increased with increasing tumor size across nearly all categories. In the ER-positive (ER+) and PR-positive (PR+) group, however, patients with tumors > 50 mm had nearly identical BCSM rates (P = 0.127, P = 0.099 and P = 0.370 for 51-60 mm, 71-80 mm and > 80 mm tumors, respectively), whereas BCSM was positively correlated with tumors < 51 mm.
Conclusions: The observation of identical HRs for BCSM among patients with ER+ and PR+ tumors >50 mm underscores the importance of individualized treatment. Our findings may contribute to a better understanding of breast cancer biology.