MKI67 and Carcinoma, Lewis Lung: These findings were further confirmed in Lewis lung carcinoma CRL syngeneic model in C57BL/6 mice where application of CO for 7 days at 250 ppm daily for 1 hour in mice with established tumors led to increased phosphorylation of Erk1/2 (Figure 1C) and lower staining of proliferation marker Ki67 (data not shown).