CCND1 (encoding cyclin D1) is often not amplified and is at lower levels in BLBC [54], consistent with cyclin D1 not being required for phosphorylation of RB [55]; however, CCND3 (cyclin D3) is frequently amplified [56], and residual disease following chemotherapy of a basal-enriched cohort of TNBC shows amplification of CCND1, CCND2, and CCND3, suggesting that the cyclin D family provides a survival advantage in drug-resistant cancers [57]. This evidence concerns the gene RB1 and cancer.