In this study, one lung adenocarcinoma cell line (PC9) in addition to four melanoma cell lines were tested, and rare populations of PC9 cells express high PDGFRB or FOSL1. This means that the similar profound transcriptional variability of a cell may predict cells among the population of EGFR-mutated lung cancer cells that will ultimately become tolerant to EGFR TKIs. This evidence concerns the gene FOSL1 and melanoma.