In sensitivity analyses, similar associations between trastuzumab receipt and deprivation were observed when restricting analyses to a HER2+ breast cancer diagnosis after mandatory SACT submission (April 2014; sensitivity analysis 1; IMD 5 vs. IMD 1; mvOR 0.93; 95% CI, 0.84–1.03; LRT P = 0.009) and were more defined when the refined HER2+ breast cancer definition (sensitivity analysis 2) was applied (IMD 5 vs. IMD 1; mvOR 0.86; 95% CI, 0.78–0.95; LRT P = 0.009). The gene discussed is ERBB2; the disease is breast carcinoma.