CDK4 and neoplasm: The activity of major tumor suppressors, RB1 and TP53 is generally conserved in luminal and HER2 enriched subtypes, while about 20% of triple negative BC (TNBC) lack functional Rb protein, making the use of CDK4/6 inhibitors more challenging; however, the luminal androgen receptor (LAR) subgroup, a subtype of TNBC, might be sensitive to inhibition of CDK4/6 pathway due to the association of AR expression and RB1 expression [4,22].