Tumor subtype was significantly associated with pain subscores at baseline and across all time points (P < .001); compared with patients with hormone-receptor-negative/ERBB2-positive disease, those with hormone-receptor-positive/ERBB2-positive or triple-negative disease reported greater between-breast differences in pain (P < .001, P = .01, respectively), by approximately 0.5 (95% CI, 0.2 to 0.9) points and 0.4 (95% CI, 0.1 to 0.7) points, respectively. Here, ERBB2 is linked to neoplasm.