Ultrastructure of the Lewis lung carcinoma.

ELectron microscopic observations were made on the Lewis lung carcinoma, which has frequently been used in various experiments. Although the tumor cells had desmosomes, interdigitation, microvilli and basement membranes which were of epithelial nature, they did not show either squamous or adenomatous differentiation. On the basis of microscopic and ultrastructural findings, this tumor falls into the category of large cell carcinomas. At the periphery of the tumor, sinusoidal clefts between the strands of tumor cells contained many red blood cells without fibrin. While perfect blood vessels were observed towards the center of the tumor, large necrotic areas were observed. Dilated large vessels possessed some endothelial fenestrations. Light endothelial cells were also observed, which were penetrated by red blood cells. Interstitial components were very scant and collagen fibres were frequently observed to be dissolved.