Here, we wanted to investigate the potential pro-tumorigenic, or pro-survival, properties of p21 in NSCLC since a high level of p21 protein correlates with a worse prognosis in this disease (Fig. 1a) and we hypothesised that p21 may provide a fitness advantage to NSCLC cells by allowing tumour cells with replication stress that persists beyond S-phase, to enter a p21-dependent quiescent state (G0) after mitosis (Fig. 1b [8–11]). The gene discussed is CDKN1A; the disease is neoplasm.