VASCULAR INVASION OF O-1N, HAMSTER SQUAMOUS-CELL CARCINOMA WITH HIGH-POTENTIAL OF LYMPH-NODE METASTASIS - ULTRASTRUCTURAL COMPARISON BETWEEN LYMPHATICS AND BLOOD-VESSELS

The ultrastructural modes of lymphatic and blood vessel invasions were studied comparatively in hamsters with squamous cell carcinoma (0-1N) that had a high potential for lymph node metastasis. The endothelial injury, which was caused by mechanical stretching with the growth of 0 -1N, was the initial and characteristic feature common to both vascula r invasions. Tumor cell nests penetrating the lymphatic lumen through disrupted endothelial cells still maintained their volume and continui ty to the underlying tumor cell nests. In contrast, pronounced microth rombotic and neutrophilic reactions occurred at the site of blood vess el penetration. Within the lymphatic lumen, large clusters of 0-1N cel ls were kept longer in spite of lymphocytic and macrophagic reactions. In blood vessels, clusters of tumor cells that had passed through den se fibrin layers were reduced in size and further disintegrated into s maller pieces by neutrophils, In conclusion, lymphatic invasion is a m echanical process, and smooth and direct invasion of large tumor cell nests into lymphatic vessels is responsible for causing more prompt an d frequent lymph node metastasis in 0-1N than a hematogenous type.