First heterotransplantation of a human carcinoid tumor into nude mice

The first successful heterotransplantation of a human carcinoid tumor into nude mice is reported. CSH, a voluminous hepatic metastasis of a primary bronchial carcinoid tumor (CSB) was resected and transplanted into three irradiated nude (Swiss-nu/nu) mice both by subcutaneous (SC) and intramuscular (IM) routes; the success rate was five of six. Heterotransplanted tumors took 4 to 5 months to appear in the mice and 1 month to attain a width of 0.5 cm. Both human and mouse tumors (named CSH-SC and CSH-IM) were studied by light and electron microscopy. They were Grimelius-positive, neuron-specific enolase-positive, and bombesin-negative by immunocytochemistry. Furthermore, CSH-SC cells presented characteristic (pear-shaped, rod-shaped, or tadpole-shaped) neurosecretory granules. Although CSB and CSH were slightly serotonin positive by immunocytochemistry, only a few serotonin-positive cells were found in CSH-SC and none in CSH-IM, suggesting partial loss of differentiation or an increase in serotonin catabolism during transplantation.