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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.