MKI67 and neoplasm: Consistent with our prior observations during the early stages of tumor initiation/progression, the tumor shrinkage produced by TMX-induced SOS1 ablation in preexisting, fully developed, tumors was also mechanistically associated to a significant reduction of cell proliferation (Ki67, Fig. 4c) and ERK phosphorylation (Fig. 4d) in the SOS1-deficient tumors.