A comparative study of smooth muscle tumors utilizing light and electron microscopy, immunocytochemical staining and enzymatic assay.

A comparative study of eight benign and eight malignant soft tissue spindle cells tumors was done utilizing light and electron microscopy, immunocytochemical staining, and enzymatic assay of tumor homogenates. The tumors were evaluated with two antibodies using both immunofluorescent (IF) and immunoperoxidase (IP) techniques. One antibody, purified rabbit antichicken gizzard myosin antibody (RAMA) delineated only smooth muscle tumors, both benign and malignant. IP was more sensitive than IF using this antibody. Nonmyogenic spindle cell tumors, which served as controls, gave uniformly negative results when stained with this antibody. The second antibody, human antismooth muscle antibody (HASMA), was not as sensitive or specific as RAMA by both IF and IP techniques. Creatine phosphokinase (CPK) isoenzyme assay revealed that both benign and malignant smooth muscle tumors contain a high content of brain and smooth muscle (BB) isoenzyme (skeletal muscle isoenzyme (MM)/BB ratio less than 0.05). In contrast, control nonmyogenic spindle cell tumors exhibited MM/BB ratios of 0.1 or greater. While electron microscopy remains the major diagnostic tool to determine the histogenesis of difficult spindle cell tumors, IP staining methods with RAMA and CPK isoenzyme assay are useful in delineating tumors of smooth muscle origin.