Ultrastructural differences between synovial sarcoma and solitary fibrous tumor: comparative study in adult patients from the National Cancer Institute of Mexico.

Synovial sarcoma (SS) and solitary fibrous tumor (SFT) are entities with considerable morphological and immunohistochemical similarities that sometimes show a non-confirmatory profile (TLE1 negative, CD34 and focal or negative STAT6 and lack of specific fusion IHC markers), in which the utility ultrastructure is unknown. A cross-sectional, retrospective, analytical, nonexperimental study was carried out by the Department of Pathology of the National Cancer Institute of Mexico (INCan) e from January 1, 2009 to December 31, 2018. With 17 SFT cases with diffuse or focal CD34 and STAT6 positivity and 18 cases of SS with positive FISH molecular test t(X:18) breakapart were studied by electron microscopy of fresh glutaraldehyde fixed or paraffin-embedded tissue. The ultrastructural findings with a significant difference present in the SS were tandem tight junctions, desmosomes and abundance of dilated rough endoplasmic reticulum (RER) cisternae (p < 0.001, 0.003, and 0.001, respectively); while in the (SFT) the presence of abundant glycogen, basal lamina, long and slender cytoplasmic processes, pinocytic vesicles, hemidesmosomes, and/or dense plaques, collagen skein, and microvilli-like buds (p = 0.028, 0.005, and <0.001 for the last five). We then infer that the five distinctive markers of the SFT are the collagen skeins intermingled with cellular processes in a shape of "squid can," and the pinocytic vesicles as they were not observed in any case of SS. Conversely, tandem junctions were not found in any SFT case. Although the presence of multivesicular buds in the SFT was not significant, it had not been previously described.

Solitary fibrous tumor of the kidney.

Solitary fibrous tumor (SFT) is an unusual spindle cell neoplasm rarely described in the kidney. Usually occurring in the pleura, it has also been described in various extrapleural sites. We report a rare case of SFT of the kidney fortuitously found in a 55-year-old patient. The imaging features are illustrated. The definite diagnosis was made through histological and immunohistochemical study after radical nephrectomy.

Lines of cell differentiation in solitary fibrous tumor: an ultrastructural and immunohistochemical study of 10 cases.

BACKGROUND: Solitary fibrous tumor (SFT) is a rare ubiquitous mesenchymal neoplasm of probable fibroblastic type with a prominent hemangiopericytoma-like vascular pattern. Since their initial description as arising from the pleura, SFTs have been reported in many extraserosal sites. It is now accepted that this neoplasm is derived from mesenchymal cells but its histogenesis is still not known. METHODS: The authors gathered clinical data on 10 patients with SFT. Tissue microarrays were constructed to perform inmunohistochemical tests and we reviewed hematoxilin-eosin-stained slides. Electron-microscopically collected samples were fixed with formalin or Karnovsky reactive and embedded in epoxy resin. RESULTS: The histopathological review showed varying degrees of cell density and mitotic activity, which correlated with clinical behavior. Immunohistochemically most tumors stained positively for vimentin, CD99, and CD34. Ultrastructural study showed some degree of myofibroblastic differentiation in all cases and focal smooth muscle features. In addition, 9 cases showed perivascular undifferentiated cells. CONCLUSION: SFT is an uncommon neoplasm with different histological patterns and clinical behavior. The authors hypothesize that the perivascular undifferentiated cells that most cases showed might correspond to a quiescent stage of adult stem mesenchymal cell and could be the target of the molecular aberrations implied in its pathogenesis.

Solitary fibrous tumor of the anterior mediastinum: a rare extrapleural neoplasm.

Solitary fibrous tumors are uncommon spindle cell neoplasms originally thought to be restricted to the pleura. We describe a 62-year-old woman who presented with stridor and an anterior mediastinal mass. At thoracotomy, a 10.5 x 6.5 x 5.5 cm, circumscribed, firm mediastinal mass demonstrated no direct cardiac or pulmonary involvement. The tumor consisted of spindle cells organized in a patternless pattern with collagenous stroma and hemangiopericytoma-like vessels. Spindle cells were immunoreactive for CD34, CD99, desmin, vimentin and bcl-2 protein and a diagnosis of mediastinal solitary fibrous tumor was confirmed. The differential diagnosis of mediastinal solitary fibrous tumors is extensive and includes spindle cell thymoma, sarcomatoid carcinoma, malignant mesothelioma, inflammatory myofibroblastic tumor, peripheral nerve sheath tumors and various sarcomas. Despite their rarity in the mediastinum, solitary fibrous tumors can be recognized by their classic patternless morphology and immunophenotypic pattern. Their accurate classification is important, as solitary fibrous tumors are intermediate (rarely metastasizing) neoplasms that require complete surgical excision and long-term clinical follow-up for optimum therapy.