Background: Dihydropyrimidine dehydrogenase (DPD), orotate phosphoribosyl transferase (OPRT), and thymidylate synthase (TS) levels correlate with sensitivity and resistance to 5-fluorouracil (5-FU). Few data are available on these enzymes in pulmonary neuroendocrine carcinoma, because 5-FU appears to have minimal effect on such carcinomas.
Patients and methods: This study investigated 5-FU-related enzymes in large-cell neuroendocrine carcinoma (LCNEC; n = 31) and small-cell lung carcinoma (SCLC; n = 15), comparing expression levels with epithelial carcinomas including adenocarcinoma (ADC; n = 34) and squamous cell carcinoma (SCC; n = 13) obtained from 93 patients with primary lung tumors. Levels of 5-FU-related enzyme mRNA were analyzed by laser capture microdissection, compared with immunohistochemical findings and correlated with clinicopathologic factors.
Results: LCNEC and SCLC showed significantly higher TS and OPRT mRNA levels than ADC. SCLC exhibited significantly higher TS mRNA levels than LCNEC (P = .002). LCNEC displayed significantly lower DPD mRNA levels than ADC (P < .001), with a similar tendency in SCLC. SCC showed significantly lower DPD (P < .01) and higher OPRT (P < .001) mRNA levels than ADC. When we divide the data by pathology into epithelial carcinoma and neuroendocrine carcinoma, malignant potentials and prognoses correlated with mRNA levels in epithelial carcinoma, but not in neuroendocrine carcinoma. Immunohistochemically, neuroendocrine carcinomas were immunonegative for DPD. A significant correlation was found between enzymatic mRNA and protein expression for DPD (R = .500) and a weak correlation was observed for TS (R = .294).
Conclusion: Neuroendocrine carcinomas show characteristic patterns of expression for 5-FU-related enzymes, including low DPD mRNA and protein level and high TS mRNA level compared with adenocarcinomas. These results partially explain why 5-FU-based chemotherapy shows minimal efficacy against SCLC. Conversely, clinicopathological data and survival analysis indicates that 5-FU-related enzymes themselves might not affect the malignant potential of neuroendocrine carcinoma. Expressional differences in 5-FU-related enzymes among pathologies may provide valuable information for tailor-made chemotherapy.