CDK4 and cancer: Similarly, cancer cells remaining after 6 months of therapy in both discovery and validation cohort tumors lost expression of cyclin D (CCND1) and genes involved in estrogen-dependent growth (e.g., PGR and MAPT are genes associated with the luminal subtype (Kensler et al, 2019)), potentially reflecting a bypass of both endocrine and CDK4/6i treatment targets.