When comparing CCND1-amplified vs. non-amplified tumours, we found that CCND1-amplified tumours show higher expression of the proliferation gene MKI67 across all PAM50 subtypes, higher CDK4 expression in luminal B and basal-like subtypes only and lower CDK6 expression in luminal A, luminal B and HER2-enriched subtypes. The gene discussed is CDK4; the disease is neoplasm.