Failure patterns according to molecular subtype in patients with invasive breast cancer following postoperative adjuvant radiotherapy: long-term outcomes in contemporary clinical practice.

PURPOSE: Although gene expression profiling provides critical information, knowledge remains limited regarding the differential effects of molecular subtype on clinical course. This study evaluated the impact of molecular status on long-term patterns of failure in patients with non-metastatic breast cancer.
METHODS: We analyzed data from 1181 individuals with invasive breast cancer undergoing surgery plus PORT from 2003 to 2011. Molecular subtypes were defined as luminal A (LA), luminal B (LB)-HER2(-), LB-HER2(+), HER2, and triple-negative (TN) based on the 2013 St. Gallen Consensus criteria. Competing risks analysis and baseline hazard rate function plots were used to explore subtype-specific recurrence patterns.
RESULTS: The 10-year overall survival rates of LA, LB-HER2(-), LB-HER2(+), HER2, and TN groups were 96, 93, 94, 84, and 85%, respectively (P < 0.001). Distant metastatic events differed significantly according to molecular subtype (P < 0.001). In competing risks regression analysis, initial development of distant metastasis was the highest with TN tumors, followed by HER2, LB-HER2(-), and LB-HER2(+) subtypes (P = 0.005). Regarding preferential sites of distant metastasis, the risk of initial brain metastasis was significantly higher with HER2 tumors, followed by TN tumors (P = 0.001). A low-level but sustained metastatic risk increment was observed in luminal tumors, whereas TN and HER2 subtypes showed a short-term risk surge within 5 years.
CONCLUSION: From the significant impact of molecular profile on distant metastasis, subtype-specific individualization of systemic treatment and close surveillance are suggested. The preferential and long-term risk of brain metastasis in the HER2 subtype underlines the importance of alternative anti-HER2 therapies.