Malignant schwannoma occurring with Schistosoma japonicum: a case report.

An 18-year-old Filipina presented with a 28 cm retroperitoneal malignant schwannoma arising from the sigmoid colon. Histopathologic examination revealed the presence of numerous schistosome ova immediately adjacent to the tumor and throughout the submucosa. Due to the rarity of malignant schwannomas, their infrequent occurrence in young persons in the absence of von Recklinghausen's neurofibromatosis, and the presence of schistosomal ovideposition, the possible role of schistosomal infection in the development of this malignancy is discussed. This is the first reported case of a malignant schwannoma occurring together with schistosomiasis.