Morphological characterization of Lewis lung carcinoma (3LL). A light and electron microscopic study.

Primary tumor and its metastases of subcutaneously injected Lewis lung carcinoma (3LL) of the mouse were examined by light and electron microscopy. Although the optical appearance, in both cases, was of a indifferentiated carcinoma, the ultrastructural observation showed characteristic intracytoplasmic myelinoid bodies similar to those seen in type II pneumocytes in normal lung. These findings suggest that Lewis lung carcinoma is a carcinoma derived from granular pneumocytes equivalent to human alveolar cell carcinoma. The histological and embryological aspects of type II pneumocytes that could explain the histogenesis of this tumor are discussed.