CDK4 and small cell lung carcinoma: This may explain why overall survival was not enhanced by similar trilaciclib/genotoxic combinations in small cell lung cancer (Weiss et al, 2019; Daniel et al, 2020; Hart et al, 2021), which are almost always Rb null and therefore insensitive to CDK4/6 inhibitors (George et al, 2015) (in comparison, Rb inactivation is only observed in 7–20% of TNBCs (Johnson et al, 2016; Peck et al, 2021; Rocca et al, 2017)).