Malignant granular cell tumor of the radial nerve: an autopsy observation with electron microscopic and tissue culture studies.

Malignant granular cell tumor closely associated with the radial nerve in the left upper arm, was found in a 34-year old man. The tumor increased rapidly in size, was locally invasive and showed recurrence and metastases to lymph nodes and the lungs. The tumor was composed solely of granular cells and its histological features were very similar to those of benign granular cell tumors. However, considerable variation of cellular size and shape, hyperchromatic plump nuclei, and some disordered cellular arrangement were thought to be significant indications of malignancy. Ultrastructural study of the tumor revealed many lysosome-like dense granules in the cytoplasm. The presence of a few axon-like cytoplasmic processes between granular cells and the intimate anatomical association of the tumor with the radial nerve seemed to support the concept of peripheral nerve origin of the malignant granular cell tumor.