ERBB2 and triple-negative breast carcinoma: In this population-based cohort of 3916 patients with de novo MBC, 14.0% required radiotherapy for BRM; this proportion was highest among patients with ERBB2 (formerly HER2)–positive/hormone receptor (HR)–negative (34.7%), ERBB2-positive/HR-positive (28.1%), and triple-negative breast cancer (TNBC; 21.9%).