AIM To establish a relevant animal model ofhuman gastrointestinal cancer,which can beused for repetitive investigations,so as toimprove our understanding and management ofcarcinogenesis and cancer metastasis.METHODS Intact tissues of human colorectaland pancreatic cancers were transplanted innude mice.The biological characteristics of theoriginal and the corresponding transplantedtumors were investigated by HE staining,PASstaining and immunostaining.The metastases inthe livers and lungs of nude mice wereinvestigated by immunostaining withbiotinylated mab KL-1 and by RT-PCR using CK20specific primers.RESULTS There were totally 9 of 16 surgicalspecimens growing in nude mice subcutaneouslyand/or orthotopically(4 of 6 colorectal and 5 of10 pancreatic cancer).Tumor cell content of thespecimens and freezing of tissue specimens areimportant factors influencing the growth oftransplanted tumor.In the group of fresh tumortissues with greater than 50% tumor cell content,the success rate of the transplantationwas 100%(3 cases of pancreatic cancer and 3cases of colorectal cancer).The orthotopicallytransplanted tumors resemble the original tumormorphologically and biologically,including TAAexpression such as CEA byimmunohistochemistry,and CEA level in theserum of mice.Ki-67 labeling index and theexpression of TAA especially K-ras,17-1A andRA-96,are associated with the potential of tumorgrowth in nude mice.Micrometastases in thelungs and livers of tumor bearing mice can bedetected by immunostaining with biotinylatedmab KL-1 and CK20-specific RT-PCR.CONCLUSION An orthotopic transplantationmodel for human colon and pancreatic cancer innude mice has been set up.We have alsoestablished sensitive detection methods withCK-immunohistochemistry and CK20-RT-PCR tostudy xenotransplanted human cancer and itsmetastatic cancer cells in the liver and lung ofnude mice.This study may be helpful inunderstanding the mechanism of cancermetastasis and in developing new diagnosticmethods and therapeutic strategies formetastases including micrometastases. AIM To establish a relevant animal model ofhuman gastrointestinal cancer,which can beused for repetitive investigations,so as toimprove our understanding and management ofcarcinogenesis and cancer metastasis.METHODS Intact tissues of human colorectland pancreatic cancers were transplanted innude mice.The biological characteristics of theoriginal and the The transplanted tumors were investigated by HE staining, PASstaining and immunostaining. The metastases in the livers and lungs of nude mice wereinvestigated by immunostaining withbiotinylated mab KL-1 and by RT-PCR using CK20specific primers.RESULTS There were totally 9 of 16 surgicalspecimens growing in nude mice Subcutaneouslyand/or orthotopically(4 of 6 colorectal and 5 of10 pancreatic cancer).Tumor cell content of the species and freezing of tissue specimens areimportant factors influencing the growth oftransplanted tumor.In the group of fresh tumortissues with greater than 50% tumor cell content,the Success rate of the tr Ansplantationwas 100%(3 cases of pancreatic cancer and 3cases of colorectal cancer).The orthotopicallytransplanted tumors resemble the original tumor morphologically and biologically,including TAAexpression such as CEA byimmunohistochemistry,and CEA level in theserum of mice.Ki-67 labeling index and the expression of TAA Specifically K-ras,17-1A and RA-96,are associated with the potential of tumorgrowth in nude mice.Micrometastases in thelungs and livers of tumor bearing mice can be detected by immunostaining with biotinylatedmab KL-1 and CK20-specific RT-PCR.CONCLUSION An orthotopic transplantation model for human colon and pancreatic cancer innude mice has been set up.We have also established sensitive detection methods withCK-immunohistochemistry and CK20-RT-PCR tostudy xenotransplanted human cancer and itsmetastatic cancer cells in the liver and lung ofnude mice.This study may Be helpful inunderstanding the mechanism of cancermetastasis and in developing new diagnosticmethods and therapeuTic strategies for metastases including micrometastases.