Frequency of metastasis depending on histologic type of primary lung carcinoma in rats.

A total of 123 malignant lung tumors (97 adenocarcinomas, 23 adenosquamous carcinomas and 3 squamous cell carcinomas) were induced in Han:WIST rats by 25 weekly subcutaneous injections of dipentylnitrosamine (DPNA). 43% of these adenocarcinomas and 87% of the adenosquamous carcinomas metastasized into various organs. The three squamous cell carcinomas showed no metastatic spread. More than half (65%) of the metastases from the adenosquamous carcinomas were composed of adenocarcinomatous components alone. Thus, the general acceptance in humans that pulmonary adenocarcinomas tend to metastasize more frequently than squamous cell carcinomas was proved in experimental animals.