MKI67 and neoplasm: The prevalent role of SOS1 over SOS2, in KRASG12D-driven LUAD development in mice was also consistent with the significant reduction of cellular proliferation (Ki67-positive tumor cells, Fig. 2a) and ERK activation (pERK levels, Fig. 2b) observed by IHC in lung tumors from 5-months-old SOS1KO mice as compared to similarly aged SOS1/2WT or SOS2KO mice.