RB1 and neoplasm: Researchers have developed and analyzed several genetically engineered mouse models (GEMMs) of SCLC [1,4,13,14], murine cell lines, and sources of subcutaneous transplantation tumors [15,16], patient-derived (PDX) [17,18] and circulating tumor cell-derived (CDX) [19], including our own K5-QKO SCLC mouse model, in which specific ablation of the four tumor suppressors Rb1, Rbl1, Pten, and Trp53 in basal epithelial airway keratin K5 expressing cells led to SCLC with a remarkable resemblance to its human counterpart [14,20,21].