Granular cell myoblastoma. A histological and enzymatic study.

Tissue from ten lesions of granular cell myoblastoma was studied. One tumor was located in striated muscle and allowed comparison of enzymatic reactions of granular cells and muscle cells in the same tissue sections. The reactions of granular tumor cells with acid phosphatase, aminopeptidase, indoxyl acetate esterase, and succinic dehydrogenase were strikingly different from those of striated muscle cells. The granules in the cytoplasm of the tumor cells showed reactions consistent with a sialomucin-protein complex, glycolipid, or ribonucleic acid. The Movat pentachrome stain was especially useful in distinguishing granular cells from stromal and inflammatory cells. The striking differences in enzymatic reactions of granular tumor cells from skeletal muscle cells rule against their origin from striated muscle. The results are consistent with the origin of the tumor cells from nerve sheath Schwann cells, fibrocytes, or histiocytes.