Malignant Smooth Muscle Tumors of the Gastrointestinal Tract: An Ultrastructural Study of 20 Cases

Twenty malignant soft tissue tumors arising from the stomach or intestine have been studied by light and electron microscopy, and the clinical records of each patient reviewed. The tumors were all considered to be of smooth muscle origin by light microscopy: Ten were spindle cell and ten were epithelioid neoplasms. By electron microscopy, only five tumors possessed smooth muscle features. A sequence of dedifferentiation could be traced among the remaining cases, indicating that the epithelioid tumors are of smooth muscle derivation. Awareness of the broad spectrum of fine structure displayed by these neoplasms will facilitate their ultrastructural identification.