Dedifferentiated leiomyosarcoma of the retroperitoneum, report of a case with immunohistochemical and ultrastructural study.

ABSTRACT

Dedifferentiated leiomyosarcoma is referred to well-differentiated leiomyosarcoma with presence of pleomorphic malignant fibrous histiocytome - like portion. A case of this tumour of the retoperitoneum was reported in a 75-year-old Thai woman who complained of 2 months of right sided abdominal pain. The 8 cm well-circumscribed mass adherent to the aorta and right ureter was found. Removal of the tumour with cauterization of the remaning fibrous tissue was performed. The patient died 3 months later with recurrence of the tumour and metastasis. Pathological examination revealed well-differentiated leiomosarcoma with abrupt change into malignant fibrous histiocytoma – like tumour. The pleomorphic multinucleated giant cells had immunoreactivities for vimentin, alpha-1-antitrypsin and alpha-1-antichymotrypsin. Very few cells stained with smooth muscle actin. Ultrastructural features were those of undifferentiated cells with rare poorly developed microfilaments with dense aggregate-like area. The findings were similar to one dedifferentiated leiomyosarcoma of the intestinal tract reported by Fakuda et al. The immunohistochemical and ultrastructural study of the dedifferentiated portion reflected malignant fibrous histiocytoma-like features (myofibroblastic) or differentiation toward smooth muscle.