摘要Background: To study novel treatment modalities for pancreatic ductal adenocarcinoma (PDAC), we need to transfer the knowledge from in vitro to in vivo . It is important to mirror the clinical characteristics of the typically local invasive growth of pancreatic cancer and the distant spread resulting in liver metasta- sis. Notably, for xenotransplant studies using human specimen, two models, i.e. subcutaneous (s.c.) and orthotopic (o.t.) transplantation are widely used.Methods: The subcutaneously and orthotopically inoculated Colo357 Bcl-x L cell-derived tumors were di- rectly compared with and without TNF-related apoptosis inducing ligand (TRAIL) treatment. The size of primary tumors, number of liver metastasis and the histologic markers Ki67, M30, TNF- α and CD31 were assessed. Results: Upon TRAIL treatment, the primary tumors did not change their size, neither in the s.c. nor in the o.t. approaches. But when s.c. was compared to o.t., the size of the s.c. tumors was more than two- fold bigger than that of the o.t. tumors ( P < 0.01). However, mice with orthotopically inoculated PDAC cells developed liver metastasis upon TRAIL treatment much more frequently ( n = 13/17) than mice with subcutaneously inoculated PDAC cells ( n = 1/11) ( P < 0.01). As a likely driving force for this increased metastasis, a higher TNF- α staining intensity in the o.t. tumors was observed by immunohistochemistry. Conclusions: These data from a direct side-by-side comparison underline the importance of the proper inoculation site of the PDAC cells. Local invasion and liver metastases are a hallmark of PDAC in the clinic; the o.t. model is clearly superior in reflecting this setting. Moreover, a serious side-effect of a possible new therapeutic compound became obvious only in the o.t. model.