Dedifferentiated leiomyosarcoma of the intestinal tract: histological, ultrastructural and immunohistochemical examinations.

Six cases of dedifferentiated leiomyosarcoma of the small and large bowel are presented with histological, ultrastructural and immunohistochemical examination. One case arose in the jejunum, two in the ileum, and the other three in the large intestine. The tumours were submucosal in four cases with large areas of ulceration; two were polypoid. Four tumours showed typical leiomyosarcomatous appearance with dedifferentiated components and two were typical leiomyosarcomas at the primary site with differentiated components only in metastatic foci. By immunohistochemistry, typical leiomyosarcomatous areas showed a positive reaction for muscle-specific actin (MSA), MB1, MB2 and myosin. In contrast, desmin-positive cells were scattered throughout the tumour or were not present. Tumour cells in dedifferentiated components were positive for alpha-1-antitrypsin and alpha-1-antichymotrypsin in all cases but one; neuron specific enolase, MB1, MB2 and myosin were positive with variety. MSA was faintly positive in only a few tumour cells of two cases and desmin was not detected in any of the cases studied. Ultrastructurally, tumour cells in typical leiomyosarcomatous areas demonstrated evident smooth muscle features, although in dedifferentiated areas they lacked such features except in one case. Our results indicate that dedifferentiated elements may derive from ordinary leiomyosarcoma and loose muscle features due to dedifferentiation.