MKI67 and neoplasm: During early tumor development, we observed an unexpected increase in tumor size following Regorafenib treatment (1.8% vs. 4.8% of the total pancreas area; p = 0.04) (Fig. 2b), accompanied by a significantly increased Ki-67 positivity index with 62% vs. 33% positive nuclei in Regorafenib- compared to PEG-treated control mice (p = 0.02) (Fig. 2c; see Ki-67 staining of the total pancreas in Supplementary Fig. S6a).