In vivo growth of activated MEK1 tranfected cells. Mock transfected (pUSE-9 and pUSE-12) and activated MEK1 (H-MEK1-15 and H-MEK1-17) clones were subcutaneously injected on both flanks of male SCID mice as described under Experimental Procedures. Tumor growth was measured and calculated as described under Experimental Procedures. Tumor volume at a given time for mock transfected clones and activated MEK1-transfected clones is plotted and shown. Differences in tumor volume between mock-transfected and activated MEK1-transfected clones were statistically significant at p < 0.01 as analyzed by ANOVA test.