Most other genes regulating pyrimidine metabolism and FP activity including UCK1, UPP1, UPP2, and DUT displayed <2-fold changes in expression in SCLC, a notable exception being TYMP, which encodes thymidine phosphorylase (TP), which is significantly downregulated in our SCLC samples. This evidence concerns the gene UPP1 and small cell lung carcinoma.