Ossifying fibromyxoid tumor: modified myoepithelial cell tumor? Report of three cases with immunohistochemical and electron microscopic studies.

Ossifying fibromyxoid tumors (OFMT) are rare soft tissue tumors of uncertain histogenesis and clinical behavior. Since Enzinger, Weiss, and Liang first described 59 examples in 1989 (Am Surg Pathol. 13:817-827), approximately 150 cases have been reported. Their clinicopathologic features are fairly well characterized and their histogenesis remains unknown. Three examples of soft tissue tumors with typical histopathologic characteristics of OFMT were studied: case 1, a 43-year-old female with a 2.5-cm tumor of the back; case 2, a 56-year-old man with an 8-cm thigh mass; and case 3, an 81-year-old female with a 13.5-cm buttock tumor. For immunohistochemistry, formalin-fixed, paraffin-embedded tissue sections were stained with antibodies against cytokeratin, smooth muscle actin, desmin, vimentin, S-100 protein, EMA, and collagen type IV using standard ABC-peroxidase methods. For electron microscopy, tissue samples fixed in EM-grade buffered formalin were processed according to routine methods. Immunohistochemistry showed that the tumor cells were positive for vimentin and S-100 protein in all 3 cases. Stains for collagen type IV revealed diffusely positive staining in the stroma with a tendency for stronger staining around the cell borders in 2 out of 3 cases. Desmin was positive in one and actin was positive in one other case. By electron microscopy, tumor cells were characterized by centrally located round to oval nuclei with varying amounts of cytoplasm containing scanty cytoplasmic organelles. There were rare profiles of rough-surfaced endoplasmic reticulum (RER) and rare mitochondria with areas of condensed intermediate filaments. No tonofilaments or actin filaments were present. There were multiple short web-like processes, some of which were attached to that of neighboring cells by primitive cell junctions. In all 3 cases, lesional cells showed external lamina (EL), which was abundant in case 1, forming redundant scrolls frequently. In case 2, EL was less prominent and incomplete, and interrupted portions of EL were present only along the periphery of cell columns or nests bordering the stroma. In case 3, which behaved as a malignant tumor, the tumor cells were less differentiated spindle cells with primitive cellular features, and EL was rarely found along the short span of tumor cell borders. In this study, tumor cells in OFMT were polygonal to stellate often with multiple short cytoplasmic processes. The tumor cells were found to form cell clusters attached by primitive intercellular junctions between cytoplasmic processes forming intercellular bridges. The cell borders facing the stroma around cell clusters tended to be flat and had incomplete EL, while no EL was present along the cell borders facing the inner aspect of cell clusters. These ultrastructural findings together with immunophenotypic expression of S-100 protein presented closer resemblance to those of modified myoepithelial cells in pleomorphic adenomas of salivary glands and skin appendages rather than peripheral nerve sheath tumors. The authors conclude that these findings render more support to the hypothesis of myoepithelial histogenesis of OFMT. They also conclude that ultrastructural study not only helps accurate diagnosis, but also may aid in predicting malignant behavior by the degree of deviation from the typical examples of OFMT.

Bednar tumor: report of a case with immunohistochemical and ultrastructural study.

A slowly growing tumor in the right shoulder of a 38-year-old white male, which felt like a superficial cystic mass, was studied. The spindle cells, which represented the main component of the tumor, were arranged in a typical storiform pattern and were positive for CD34 and focally for CD117. The pigmented cells were mostly found at the center of the storiform whorls and were negative for S-100 protein and HMB-45. Ultrastructurally, the tumor consisted predominantly of nondescript mesenchymal spindle cells that resembled fibroblasts. The tumor cells blended into a loosely arranged stromal tissue background. The general appearance of pigmented cells was very similar to the nonpigmented spindle cells. The pigment appeared to be a mature form of melanin granules. The lack of premelanosomes, cell injections, basal lamina, and pinocytotic vesicles was inconsistent with a neural origin/neural differentiation hypothesis for this tumor.

Postirradiation epithelioid angiosarcoma of the breast: a case report with immunohistochemical and electron microscopic study.

A case of postirradiation epithelioid angiosarcoma of the breast in a 72-year-old woman is reported. She had had right breast conserving surgery, axillary lymph node dissection, and 50 Gy external beam radiation therapy for infiltrating ductal carcinoma. A skin lesion on the irradiated breast appeared 5 years after completion of radiation. Angiosarcoma was diagnosed in a contralateral axillary mass 8 months later. Light microscopically, the tumor was characterized by a sheet-like growth of epithelioid cells with focal vasoformative areas. Tumor cells were reactive for factor VIII-related antigen, cytokeratin and CD34. Electron microscopically, the tumor cells were round with smooth cell borders. They were closely apposed, occasionally forming a small lumen containing single red blood cells or aggregates of platelets. Groups of tumor cells were enclosed by an external lamina. The tumor cells had abundant cytoplasm with sparse organelles. Rare suggestive Weibel-Palade bodies were present. The immunohistochemical and ultrastructural findings in this postirradiation tumor were in agreement with previously reported findings in non-irradiation-induced epithelioid angiosarcomas.

Peculiar cytoplasmic inclusions in oncocytic adrenal cortical tumors: an electron microscopic observation.

Two cases of an oncocytic adrenal cortical tumor that contained peculiar cytoplasmic crystalline inclusions in the tumor cells are presented. The patients were 49- and 72-year-old females without clinical and biochemical evidence of adrenal cortical or medullary dysfunction. The adrenal tumors weighed 80 and 200 g each. These crystalline inclusions were present in groups of longitudinal profiles or clusters of crossly cut aggregates. They appeared in clusters of membrane-bound columns. On longitudinal sections, they appeared as rigid rods of homogenous density measuring 36 nm in width, but when they were cut transversely their paracrystalline nature became apparent. They were composed of closely packed microtubules in rectangular blocks. The microtubules measured 12.5 nm with a hollow center measuring 4.2 nm. The inclusions were within the membrane-bound cisterna of rough-surfaced endoplasmic reticulum. The significance of these inclusions is not clearly understood; however, they have been seen only in adrenal cortical tumors and their presence may be helpful in the differential diagnosis of adrenal oncocytic tumors. One patient presented with a tumor in which gross and microscopic appearance was compatible with a pheochromocytoma. This case exhibited an oncocytic appearance and pronounced cellular pleomorphism. Ultrastructural studies were necessary to recognize the tumor cells as cortical cells. The tumor cells contained abundant mitochondria with tubular cristae, paranuclear parallel stacks of granular endoplasmic reticulum, and relatively prominent smooth endoplasmic reticulum. These features are typical of adrenocortical cells. In addition, frequent tumor cells contained the peculiar cytoplasmic inclusions herein described.