Four spontaneous tumors have been discovered by accident in using nude mice as host for human tumors xenograft from 1981 to 1995. lts morbidity is about 0.14%(4/2850).Three of the four cases were identified as B cell lymphomas by pathological morphology and immunohistochemistry. Tumor cells mainly occured in lymph node and apleen
and local invasion was seen in liver
kidney and lung. The other one was squamous cell carcinoma of anal canal. The four tumors are all murine origin and the human tumors xenografted into these nude mice were unable to grow . The present study discussed the morbidity of spontaneous tumor and pathological patterns
the etiology of apontaneous tumor
and the relationship between the spontaneous tumor and the xenografted human tumors.