Malignant mixed tumor (carcinosarcoma) of the pancreas: a case report supporting organ-induced differentiation of malignancy.

Background: We present an unusual case of a malignant mixed tumor (carcinosarcoma) of the head of the pancreas that was surgically resected and whose tissue pathologic condition supported the concept of organ-induced differentiation of malignancy.
Methods: After a pancreaticoduodenectomy, tissue sections from various anatomic regions of the tumor were studied by routine histologic examination and immunocytochemistry. Genomic DNA from various regions of the tumor was extracted and digested with Hpa II, and a 511 bp region of the hypoxanthine phosphoribosyltransferase gene was amplified with the polymerase chain reaction to assess clonality.
Results: The pathologic findings revealed areas of both adenocarcinoma and leiomyosarcoma, but these disparate areas were not randomly distributed but rather were polar in nature. The adenocarcinomatous areas localized to the tumor within the head of the pancreas, an area of normal ontogenetic glandular development, whereas the leiomyosarcomatous areas localized to regions of the tumor infiltrating the duodenal wall, an area of normal ontogenetic smooth muscle development. Both the adenocarcinomatous and the leiomyosarcomatous areas showed evidence of monoclonality and clonal identity.
Conclusions: This interesting polar distribution of histologic patterns illustrated by this malignant mixed tumor (carcinosarcoma) supports the hypothesis of organ-induced differentiation of malignancy.