WNT ligands constitute a family of at least 19 highly conserved, secreted, cysteine-rich glycoproteins. They have been divided into two different groups based on their ability to induce transformation of cells. WNT5A is one of the best investigated members of the non-transforming WNT protein-group and is therefore associated with the so called non-canonical signaling pathways. However, the precise role of WNT5A in tumorigenesis remains ambiguous. For example in colorectal cancer and ductal breast cancer WNT5A is considered to be a tumor suppressor and its loss is an independent factor predicting poor prognosis. In contrast WNT5A has been identified as a potent enhancer of malignant progression in pancreatic cancer. Previous data of this group has demonstrated antiapoptotic, pro-migratory and pro-invasive effects of WNT5A on pancreatic tumor cells. In this context WNT5A surprisingly activated the canonical cascade, while failing to signal via the WNT/Ca2+ pathway. This dissertation was able to demonstrate that the antiapoptotic effects of WNT5A are not restricted to pancreatic cancer cells. At least in MDA-MB-468 breast cancer cells a knock-down of WNT5A led to an increase in basal and TRAIL-induced apoptosis. In addition, the antiapoptotic effects of WNT5A in pancreatic cancer could be confirmed in experiments with recombinant WNT5A. Treatment with rmWNT5A reduced the rate of gemcitabine-induced apoptotic cell death significantly. At the same time WNT5A had no impact on SAPK/JNK in PaTu-8988t cells, underlining the importance of the canonical cascade for WNT5A signaling in pancreatic cancer. In vitro experiments are not sufficient to evaluate the use of WNT5A and other genes for new therapeutical applications. A well established strategy for in vivo evaluation is the generation of xenografts in athymic nude mice by implanting human tumor cells that are stably or conditionally transfected with the gene of interest. A methodical challenge of xenograft experiments is that only the growth of subcutaneous xenografts can be easily measured. In case of pancreatic cancer in vivo imaging of orthotopic xenografts is difficult. The establishment of sodium/iodide symporter (NIS) expressing xenografts from pancreatic tumor cells is a completely new approach, because NIS expressing tumor cells can be visualised via SPECT following i.v. injection of 99mTc pertechnetate. In this dissertation three pancreatic cancer cell lines have been stably transfected with NIS Imim-Pc1 RV/NIS, PaTu-8988t pBig2R/WNT5A NIS and PaTu-8988t pBig2R NIS. Subsequently a small group of athymic nude mice has been subcutaneously injected, each with one of the three cell lines to establish xenografts. Unfortunately, only xenografts from Imim-Pc1 cells showed sufficient growth to perform a 99mTc pertechnetate SPECT scan. This dissertation demonstrates that in vivo imaging of NIS expressing pancreatic cancer cell xenografts is feasible, therefore providing a basis for further experiments with orthotopic xenografts.