We found that rectal GISTs arise predominantly in the lower half of the rectum and have high CD117 and CD34 expression. Local resection may be a good choice for very-low-risk and low-risk GISTs, but aggressive surgery may be more beneficial for high-risk and intermediate-risk GISTs. For patients with disease recurrence, the results of secondary surgery were poor. Only the NIH risk classification proved to be an independent prognostic factor for rectal GISTs, whereas the proof for other factors was insufficient.

AIM To establish a relevant animal model of human gastrointestinal cancer, which can be used for repetitive investigations, so as to improve our understanding and management of carcinogenesis and cancer metastasis. METHODS Intact tissues of human colorectal and pancreatic cancers were transplanted in nude mice. The biological characteristics of the original and the corresponding transplanted tumors were investigated by HE staining, PAS staining and immunostaining. The metastases in the livers and lungs of nude mice were i n v e s t i g a t e d b y i m m u n o s t a i n i n g w i t h biotinylated mab KL-1 and by RT-PCR using CK20 specific primers. RESULTS There were totally 9 of 16 surgical s p e c i m e n s g r o w i n g i n n u d e m i c e subcutaneously and/or orthotopically (4 of 6 colorectal and 5 of 10 pancreatic cancer). Tumor cell content of the specimens and freezing of tissue specimens are important factors influencing the growth of transplanted tu m o r . I n t h e g r o u p o f f r e s h t u m o r tissues with greater than 50% tumor cell content, the success rate of the transplantation was 100% (3 cases of pancreatic cancer and 3 cases of colorectal cancer). The orthotopically transplanted tumors resemble the original tumor morphologically and biologically, including T A A e x p r e s s i o n s u c h a s C E A b y immunohistochemistry, and CEA level in the serum of mice. Ki-67 labeling index and the expression of TAA especially K-ras, 17-1A and RA-96, are associated with the potential of tumor growth in nude mice. Micrometastases in the lungs and livers of tumor bearing mice can be detected by immunostaining with biotinylated mab KL-1 and CK20-specific RT-PCR. CONCLUSION An orthotopic transplantation model for human colon and pancreatic cancer in nude mice has been set up. We have also established sensitive detection methods with CK-immunohistochemistry and CK20-RT-PCR to study xenotransplanted human cancer and its metastatic cancer cells in the liver and lung of nude mice. This study may be helpful in understanding the mechanism of cancer metastasis and in developing new d i a g n o s t i c m e t h o d s a n d t h e r a p e u t i c s t r a t e g i e s f o r m e t a s t a s e s i n c l u d i n g micrometastases.