Metastatic involvement of the peritoneum is not a very rare autopsy finding. Clinically, however, peritonitis carcinomatosis from a lung cancer is infrequently encountered and the pattern of the metastasis has not been studied. A total of 1041 patients with lung cancer who were admitted to our division over a 26-year period were retrospectively analyzed. Twelve (1.2%) of the 1041 patients with advanced lung cancer developed peritoneal carcinomatosis in their clinical courses. The incidence of peritoneal carcinomatosis was high in patients with large cell carcinoma and adenocarcinoma. Six and 9 of the 12 patients had metastases in intra-abdominal sites and pleural seeding, respectively. The median survival time from the diagnosis of peritoneal carcinomatosis was 2 months. Ascites accompanying metastasis to abdominal organs and pleural seeding in a patient with a known lung cancer would be regarded as a metastasis.

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