To determine to what extent TP plays a role in sensitivity to these fluoropyrimidines, we modulated TP activity in several colon cancer cell lines and one non small cell lung cancer (NSCLC) by inhibiting TP activity with TPI, and/or by overexpression of TP via stable transfection with a plasmid containing the cDNA for TP. The gene discussed is TYMP; the disease is colonic neoplasm.