Malignant Solitary Fibrous Tumor of the Humerus: A Case Report of an Extremely Rare Primary Bone Tumor

Solitary fibrous tumor (SFT) is a spindle-shaped cell neoplasm originally described in the pleura, but subsequently found in many anatomic sites. Only few cases of primary SFTs in the bone have been previously described in the literature. We present the case of an 86-year-old man with a 1-week history of pain in his left arm. Imaging studies demonstrated a well-defined osteolytic lesion in the proximal humerus measuring 6.1 cm in diameter. Sections showed a round to spindle-shaped cell neoplasm with prominent mitotic activity (28 mitoses per 10 high-power fields) and areas of necrosis, focally surrounding staghorn-shaped vessels. The tumor cells were positive for CD34, CD99, Bcl-2, and STAT6 and negative for smooth muscle actin, epithelial membrane antigen, and cytokeratin AE1/AE3. These findings were consistent with a malignant SFT involving the left humerus. Although extremely rare, SFT should be considered in the differential diagnosis of primary bone tumors. This is the first case report of a primary SFT in a long bone with malignant histological features.

A NEW CRYSTAL-CONTAINING CELL IN HUMAN ADRENAL CORTEX

Electron microscope examination of the adrenal cortex from three male human subjects revealed a special type of cell occurring in periendothelial spaces, in all adrenal cortex zones. It is a clear, spindle-shaped cell the principal cytoplasmic features of which are crystalline inclusions with a structure similar to that of the Reinke crystals of human testicular interstitial cells and an abundance of microfilaments. Enzymatic digestions with pronase, pepsin, and ribonuclease were performed, and no digestion of the crystals was obtained. The crystals had no peroxidase or acid phosphatase activities. This cell appears to be exclusive to human males and it may be related to adrenal androgen secretion.