KRAS and sarcoma: In addition, the observation of the K-ras mutation at codon 12 of exon 2 within a retroperitoneal-based, undifferentiated spindle cell malignancy is likely to indicate a pancreatic epithelial origin, particularly in cases where there is no evidence of a coexisting or preexisting well-differentiated component (eliminating ‘dedifferentiated’ sarcoma) and where the tumor lacks specific mesenchymal or epithelial immunomarker expression.