MKI67 and neoplasm: Interestingly, the rates of tumor cell proliferation (Fig. 5d) and pERK phosphorylation (Fig. 5e) levels measured within the lung tumors were not significantly affected by either SOS1 or SOS2 ablation in comparison to their SOS1/2WT/KRASWT WT controls (Fig. 5d, e), although the low levels of Ki67 expression detectable in non-tumor areas of the lung appeared to be slightly reduced in the SOS1KO samples.