Search

A 47-year-old man presented with a soft tissue mass of the distal right thigh near the knee. The tumor was highly vascular with epithelioid tumor cells growing in a peritheliomatous pattern, suggesting a soft tissue glomus tumor. Yet many tumor cells contained hemosiderin pigment and formed papillary structures suggestive of pigmented villonodular synovitis. Tumor cells were cytologically bland, and there was minimal mitotic activity. The tumor cells were strongly immunoreactive for cytokeratin, however, and contained true desmosomes, gland lumina, microvilli, tonofilaments, and well-developed basal lamina. These findings plus the absence perinuclear aggregates of intermediate filaments rule out malignant rhabdoid tumor and epithelioid sarcoma. Also, magnetic resonance imaging revealed no other lesions to suggest metastatic carcinoma. Thus this tumor appears to be a predominantly epithelioid form of monophasic synovial sarcoma. Recognition of this variant of synovial sarcoma is important for prognostication and therapeutic decision making because some studies indicate that this variant of synovial sarcoma follows a relatively benign clinical course.

A 15-year-old girl presented with a small, indolent mass near the knee joint. Light microscopy revealed a peculiar myxoid plexiform tumor composed of cytologically bland cells. Interpretation of the initial biopsy material was controversial. Subsequent immunohistochemical studies revealed tumor cells to be strongly reactive for epithelial membrane antigen (EMA) and negative for S-100 protein. Ultrastructural studies revealed tumor cells with long, thin, bipolar cell processes and discontinuous basal laminae. They had no epithelial or histiocytoid features. Admixed among the tumor cells were Schwann cells, but they represented a rare and scattered component of the overall cell population. These features are most consistent with a so-called perineurioma and contrast with those of plexiform neurofibroma and traumatic neuroma (two lesions strongly positive for S-100 protein and showing a distinctive EMA immunoreactivity pattern with focal peripheral staining of neural bundles).

A 44-year-old woman with a long history of smoking presented with a single lung mass detected on routine chest radiographs. There were no other known primary tumors. Light microscopy showed a mucin-producing adenocarcinoma of bronchioloalveolar type. Furthermore, no gastrointestinal primary has been discovered 18 months after discovery of the lung tumor. Electron microscopy revealed that tumor cells had microvilli containing abundant microfilamentous, dense-core rootlets that showed long extensions into apical cytoplasm. The microvilli were capped by numerous glycocalyceal bodies. These findings are similar to the ultrastructural features previously described as being specific for gastrointestinal adenocarcinomas metastatic to lung. The current case, however, suggests that the findings of glycocalyceal bodies and microvillous dense-core rootlets are not helpful in distinguishing between primary and metastatic lung adenocarcinomas.

A 46-year-old man presented with a cytologically bland testicular tumor composed of spindle cells that showed both epitheliallike (ie, true desmosomes and tonofilamentlike structures) and myogenous differentiation (ie, thin filaments with focal densities and alpha-smooth muscle actin immunoreactivity). Tumor cells were immunoreactive for vimentin and S-100 protein but negative for cytokeratin and desmin. Peritubular myoid cells are present in the normal testis; contain subplasmalemmal micropinocytotic vesicles; show thin filaments with focal densities; and are reactive with desmin, vimentin, and alpha-smooth muscle actin. They have no desmosomes and lie outside the basement membrane of the seminiferous tubules; thus they are not true myoepithelial cells (a cell type not present in the testis). Paradoxically, the current tumor appeared to show bidirectional differentiation, mimicking both a peritubular myoid spindle cell and an epitheliallike cell (possibly similar to the granulosa cell or rete testis epithelial cell). Although the findings suggest myoepithelial differentiation, the cytogenesis of this tumor remains uncertain.

A 57-year-old man with malaise, ascites, and abdominal pain was found to have a peritoneum studied with numerous, small nodular tumor masses. Light microscopy revealed an anaplastic malignant tumor of uncertain differentiation. Mucin stains were negative. Electron microscopy revealed pleomorphic tumor cells with diffusely distributed cytoplasmic tonofilaments and well-developed true desmosomes. No long, thin, branching microvilli were present, yet tumor cells were strongly positive for both callus keratin (polyclonal) and monoclonal cytokeratin (AE1/3) in a diffuse cytoplasmic distribution (a pattern corresponding to the diffuse cytoplasmic tonofilaments). Tumor cells were negative for Leu-M1 and carcinoembryonic antigen. The findings were most consistent with malignant mesothelioma, and additional questioning, after tissue diagnosis, revealed a work history of asbestos exposure.

Oncogenic or tumor-induced osteomalacia-rickets is a syndrome characterized by hypophosphatemia, renal phosphate wasting, and decreased serum 1,25-dihydroxyvitamin D3 levels. The tumors secrete a phosphaturic substance that causes total body phosphate depletion, leading to osteomalacia or rickets. Although the tumors are histologically polymorphous, personal review of 16 tumors documented to cause this syndrome revealed four morphologic patterns. The first contained 10 unique-appearing, mixed connective tissue tumors having variably prominent vessels, osteoclastlike giant cells, focal microcystic changes, dystrophic calcification, osseous metaplasia, and/or poorly developed cartilagelike areas. With one exception, all tumors of this group occurred in soft tissue and were benign. The single malignant tumor originated in bone, recurred locally, and metastasized to lung. The remaining tumors occurred in bone and showed benign clinical behavior. They resembled tumors known to occur in bone, that is osteoblastomalike (3 tumors), nonossifying fibromalike (2 tumors), and ossifying fibromalike (1 tumor).

A 66-year-old woman presented with a superior-anterior mediastinal mass that contained considerable calcification by computed tomography. Initial biopsy interpretation was inconclusive but suggested a giant cell sarcoma of soft parts because the tumor contained atypical epithelioid cells and osteoclastlike giant cells. After radiation and chemotherapy, the tumor was removed. It contained large epithelioid cells, pale chondroid areas, metaplastic bone, and osteoclastlike giant cells. Immunohistochemical and electron microscopic studies revealed the epithelioid cells to be factor VIII positive and to contain abundant intermediate filaments, micropinocytotic vesicles, Weibel-Palade bodies, basal lamina, and primitive cell-cell junctions. These epithelioid cells also stained for muscle-specific actin (HHF-35), yet were negative for desmin and cytokeratins (CAM 5.2 and AE1/3). The findings were most consistent with those reported to occur in epithelioid hemangioendothelioma.

A 62-year-old woman presented with an asymptomatic anterior mediastinal mass. Clinically considered to be a thymoma, the tumor was solid, firm, and composed of hypocellular dense collagen and cytologically bland, spindled fibroblastlike cells growing in a patternless pattern. There was no apparent connection to pleura or pericardium, yet the clinicopathologic features clearly fit with solitary fibrous tumor (SFT) of mediastinum. SFTs occur most commonly in pleura but have been reported in other locations, including the mediastinum, where aggressive behavior has been more common when these tumors are compared to those occurring in pleura. Although it is difficult to predict behavior for all cases of SFT occurring in the mediastinum by cytologic features alone, morphologic criteria for benign and malignant forms have been described. Roughly half the malignant forms will progress, yet the single most important indicator of clinical outcome is whether the tumor can be initially totally excised.