The unique cytologic picture of oat cell carcinoma in effusions.

Characteristic and unique patterns of the tumor cell population in pleural effusions in oat cell carcinoma have been described in detail. This pattern is constituted by rows of tumor cells or cell layers forming "vertebrae like" figures and "onion like" formations. A distinct pattern of this kind was only found in oat cell carcinoma. A distinct "oat cell carcinoma pattern" was also found in one quarter of the patients in a series of oat cell cancer with cytologic analysis of sputum. This fact may be of importance for the accurate typing of small cell undifferentiated cancer in sputum and bronchial secretions. Identical formations were also found in a histologic series of oat cell cancer. The study indicates that in small cell carcinoma of the lung it is possible by cytologic analysis of positive effusions not only to make a diagnosis of carcinoma, but also to confirm the histologic type and, thus, the origin of the tumor.