OBJECTIVETo provide an useful animal model for exploring metastatic biology and anti-metastatic therapy of primary malignant melanoma of the small intestine.

METHODSA 49-year old male patient with malignant melanoma was treated by surgery, and the primary tumor in the small intestine and a metastatic tumor in the liver were removed. The diagnosis of malignant melanoma was confirmed by histopathology. Fresh melanoma tissue fragments taken from the primary intestinal tumor and hepatic metastatic tumor were orthotopically implanted into the mucosal layer of small intestine in nude mice, respectively. The tumor growth rate, invasion and metastasis of the transplanted tumors were observed. Light and electron microscopy, immunophenotype analysis, flow cytometry and karyotype analysis were carried out.

RESULTSFragments of the primary and liver metastatic malignant melanoma were successfully implanted in nude mice. After continuous passages in nude mice, an highly-metastatic model of human primary malignant melanoma of the small intestine (from the primary lesion) in nude mice (termed HSIM-0602) and a liver metastatic model of human primary malignant melanoma of the small intestine (originally from the liver metastatic lesion) in nude mice (termed HSIM-0603) were successfully established. Histological examination of the transplanted tumors revealed a high-grade melanoma of the small intestine. Immunohistochemical stainings of S-100 protein and HMB45 were positive. Many scattered melanosomes and melanin complex were seen in the cytoplasm of tumor cells. Chromosomal modal number was between 55 and 59. DNA index (DI) was 1.59 - 1.71, representing a heteroploid. The HSIM-0602 and HSIM-0603 tumor models had been maintained for 21 and 23 passages in nude mice, respectively. 227 nude mice were used for transplantation. Both the growth rate after transplantation and resuscitation rate from liquid nitrogen cryopreservation were 100%. The HSIM-0602 model exhibited 84.8% lung metastasis, 65.7% liver metastasis and 63.8% lymph node metastasis. However, HSIM-0603 displayed 100% liver metastasis, 46.7% lung metastasis and 71.3% lymph node metastasis. The transplanted tumors actively and invasively grew in the small intestine of nude mice and showed hematogenous and lymphatic metastases.

CONCLUSIONTo our knowledge it is the first time that two strains of spontaneous highly-metastatic nude-mouse model of human primary malignant melanoma of the small intestine have been successfully established in our department. The models are very closely mimic the natural clinicopathologic course of primary small intestinal melanoma in humans and provide ideal animal models for the researches on metastasis biology and anti-metastatic experimental therapy of malignant melanoma of the small intestine.