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Some view ultrastructure as key to myofibrosarcoma diagnosis, whereas others argue that electron microscopy is too little used in contemporary practice to be considered an important diagnostic tool. These views are discussed in the context of 10 ultrastructurally confirmed cases of myofibrosarcoma, some occurring at rare sites such as skin and penis. Patient age ranged from 21 to 83 years, with a 6:4 male to female ratio. Size ranged from 2 to 7.5 cm and all had infiltrative margins. Histologically, all consisted of variably cellular fascicles of spindle cells with mild to moderately pleomorphic nuclei, small punctate nucleoli, and eosinophilic cytoplasm. All cases showed α-smooth muscle actin positivity and 2 showed very focal weak positivity for desmin. Ultrastructurally, the tumor cells contained rough endoplasmic reticulum, mainly peripheral smooth-muscle myofilaments, and fibronectin fibrils or fibronexus junctions at the cell surface. The most confident diagnosis of myofibrosarcoma is provided by ultrastructural examination. However, given the right histological appearance, use of a panel of antibodies that includes α-smooth muscle actin, desmin, and h-caldesmon, serves as an acceptable practical way of diagnosing myofibrosarcoma. [ABSTRACT FROM PUBLISHER]

Rectal/anorectal malignant melanomas are highly aggressive tumors with a poor prognosis and low 5-year survival rate. They are also very rare. Of the well-known histological variants of malignant melanoma, the small cell subtype is also very uncommon; consequently, small cell anorectal malignant melanoma is an exceedingly rare occurrence. In this article, the authors provide a detailed clinicopathological description of small cell malignant melanoma of the rectum, documenting clinical, histological, immunohistochemical, and ultrastructural features, to add to the sparse references on this tumor in the literature. The patient was a 53-year-old woman with a mass 2 cm from the anus, which was surgically removed. In histological sections, the tumor was a small cell malignant melanoma, with a tumor cell diameter of 7.6±1.0 µm, and a range of 5.5-10.7 µm (N = 100). Tumor cells were positive for S-100 protein and HMB-45 and contained sparse but unambiguous type II melanosomes. This article is one of the few detailed clinicopathological documentations of a small cell malignant melanoma of the rectum (anorectum) and the first to have the diagnosis confirmed ultrastructurally by the identification of melanosomes. The present case adds to the 3 mainly or entirely small cell anorectal malignant melanomas described in the literature. There are also at least 12 other cases with less well-defined numbers of small tumor cells or with small cells admixed with other cell morphologies. Documentation of these unusual morphological variants is important for identifying any distinctive outcome they might exhibit compared with conventional malignant melanoma. [ABSTRACT FROM AUTHOR]

An unusual leiomyosarcoma in the thigh of a 53-year-old woman is described. Tumor cells were spindled and positive for muscle immuno-markers. Some cells exhibited typical smooth-muscle ultrastructure - abundant myofilaments, focal densities, attachment plaques, plasmalemmal caveolae, and lamina. Others had fewer myofilaments and prominent rough endoplasmic reticulum. These features indicated a variable phenotype that included synthetic-phase (matrigenic) differentiation. Synthetic-phase cells were distinguished from myofibroblasts by typical smooth-muscle surface features in the absence of fibronexus junctions. In a subset of cells myofilaments were absent, but structures resembling solitary focal densities were identified. These are discussed as possible indicators of a primitive level of smooth-muscle differentiation. [ABSTRACT FROM AUTHOR]

Eighty-two mesenchymal tumors of the gastrointestinal tract were examined by electron microscopy for the purposes of subtyping for diagnostic precision and of understanding cellular differentiation. Tumors were subclassified into leiomyoma/leiomyosarcoma, tumors of the interstitial cell of Cajal (equivalent to traditionally defined GISTs [Miettinen et al. Hum Pathol. 1999; 30:1213-1220; Mod Pathol. 2000; 13:1134-1142]), gastrointestinal autonomic nerve tumors (GANTs), and fibroblastic and myofibroblastic tumors, using criteria from the literature. Leiomyoma/leiomyosarcoma were diagnosed by myofilaments, attachment plaques, plasmalemmal caveolae, and lamina; GIST by processes or cell bodies full of intermediate filaments, solitary focal densities amid intermediate filaments, attachment plaques with incomplete lamina, scarce myofilaments, and smooth endoplasmic reticulum; GANTs by neuroendocrine granules, cell bodies/processes full of intermediate filaments (more rarely microtubules), and smooth endoplasmic reticulum; fibroblastic/myofibroblastic tumors by abundant rough endoplasmic reticulum, myofilaments, and fibronexuses. Seventy-three tumors (89%) were successfully subclassified, as 5 leiomyoma/leiomyosarcoma (6%), 36 GISTs (44%), 22 GANTs (27%), 10 fibroblastic and myofibroblastic tumors (12%). Results indicated overlap between poorly differentiated leiomyosarcoma and GIST, and between GIST and GANT. GANT is emphasized as a neuronal tumor identifiable by electron microscopy, and thereby distinguishable from GIST. [ABSTRACT FROM AUTHOR]

The features of two spindle-cell carcinomas of the dermis are described with special reference to the presence of fibronexus junctions in tumour cells. The cases were of a 78-year-old man with a left eye-lid tumour and a 78-year-old woman with a naso-labial fold tumour, who had been given radiotherapy 13 years earlier for a clinically diagnosed basal cell carcinoma. Both specimens were slightly ulcerated and polypoid. Histologically, invasive tumour consisted of interlacing fascicles of plump spindled and oval cells, which were positive for several anti-cytokeratin antibodies, epithelial membrane antigen, vimentin and smooth-muscle and muscle-specific actins. Ultrastructurally, tumour cells in both cases contained rough endoplasmic reticulum (prominent in case 1), tonofibrils, desmosomes and smooth-muscle type myofilaments with focal densities. Fibronexus junctions were also present, which correlated with positive staining for fibronectin. This is the first documentation of the fibronexus in epithelial tissue in vivo, and the first unambiguous demonstration in a spindle-cell carcinoma. It extends the known distribution of the fibronexus and expands the ultrastructural spectrum of squamous carcinoma. [ABSTRACT FROM AUTHOR]

An atypical carcinoid tumor originating in the horseshoe kidney of a 39-year-old man is reported. The tumor showed cytological atypia, increased mitotic rate and histological signs of mucinous differentiation and osseous metaplasia. Even though there were distant metastases, the patient survived partial nephrectomy including resection of the primary tumor for four years. The review of literature shows that carcinoid tumors originate some 60 to 85 times more often in horseshoe kidneys than in normal kidneys. The clinical course of renal carcinoid tumors is highly variable.