To evaluate the significance of TPA (tissue polypeptide antigen) as a tumor marker for lung cancer, the present studies were designed to measure serum TPA levels as well as TPA contents in tumor tissues in patients with lung cancer. Average serum TPA levels (203.5+180.5U/l, mean+SD) in 76 patients with lung cancer (30 squamous cell carcinoma, 38 adenocarcinoma, 8 small cell carcinoma) were significantly higher than those in pneumonia (83.3+ 42.7U/l, n=13), pulmonary tuberculosis (87.6+36.3U/l,

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... =16), and normal controls (46.8+23.7U/1, n=28). There was no significant difference in TPA levels according to the histological type of lung cancer. Comparing respective stage cases, statistically significant differences were observed in serm TPA levels between normal controls and stage 1, stage 1 and stage 3, and in stage 3 and stage 4, suggesting a gradual increase in TPA levels accompanying the progress of the lung cancer. In patients with 12 squamous cell carcinoma and 9 adenocarcinoma, the TPA levels in carcinoma tissues and non-tumor invaded lung tissues were 115.2+187.7 and 148.9+223.3U/mg protein, indicating no significant difference in carcinoma and normal tissues. There was definite correlation between serum TPA levels and TPA contents in carcinoma tissues. No significant relationship, however, was observed between serum TPA levels and TPA contents in tissue not invaded by tumor. These results suggest that serum TPA levels reflect the tumor burden in patients with lung cancer. In conclusion, the determination of TPA in blood is useful for the diagnosis of lung cancer.