While the tumor cells proved to be of epithelial and human origin (Cytokeratin positive, Ku70 positive, Vimentin negative), human fibroblasts (expected to be Cytokeratin negative, Ku70 positive, Vimentin positive) could not clearly be detected 10 weeks after injection (n = 5 per xenograft type; Suppl. Here, XRCC6 is linked to neoplasm.