TYMS and neoplasm: Based on the in vitro studies demonstrating the ability of compound 19-S to inhibit TYMS catalytic activity (Figure 1B) and cause cytotoxicity in PDAC, PanNET, colon cancer, and SCLC cell lines (Figure 1C and Supplemental Figure 1, B and C), we studied the in vivo effects of compound 19-S in 2 xenograft tumor models available in our laboratory.