A histopathological study of lymphoid tissue reaction to metastatic nasopharyngeal carcinoma in nude mice.

In attempts to heterotransplant human NPc into nude mice, using seven cultured cell lines, we have succeeded in growing a carcinoma simplex, composed of Epstein-Barr virus-determined nuclear antigen-positive and Epstein-Barr virus genome-positive cancer cells, at the injected site with two of the cell lines. These originated from a spindle-cell carcinoma (Chinese NPC-204) and from a combined-cell carcinoma (Chinese NPC-501), respectively. During the first few passages, wandering macrophages were prevalent and increased in number in response to the presence of the tumours. In conjunction with a gradual decrease in the number of wandering macrophages in the medullary sinuses, diffuse hyperplasia of lymphocytes occurred in regional lymph nodes. As a result of the release of lymphocytes and macrophages into the peripheral lymph nodes, the spleen underwent extensive change, as manifested by the collapse of the splenic cords and the formation of septa studded with granulomas. Under these conditions of immunosuppression, lymphatic metastases were observed during the periods between the 11th and 14th generations and the 24th and 30th generations with NPC-204 and between the 9th and 14th generations with NPC-501. The neighbouring lymph nodes, like the spleen, were often studded with epithelioid-cell granulomas, formed by the aggregation of macrophages around nuclear debris in the subcortical areas. We assume that the clumps of debris are the remnants of metastatic cancer cells which were probably killed by macrophages or by sensitized lymphocytes. If the lymph nodes contain a barrier of granulomas, they are not invaded by tumour cells from the cortical sinuses, except in the rare case of retrograde metastasis from the hilus. It would appear that macrophages can replace T lymphocytes, which are found in very small numbers in the nude mice used in this study, in killing tumour cells and, furthermore, in protecting the lymph nodes from the spread of metastases. Metastasis cannot occur in these nude mice when their lymphoreticular system, especially that of the spleen, is working in a stable balance.