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      Subcutaneous Soft Tissue Sarcoma with Rhabdoid Features in a Dog


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          A nine-year-old male beagle dog had a white spherical mass in the subcutis of the left lumbar region. Microscopically, spindle to oval cells diffusely proliferated in the fibrous and myxoid stroma. Many neoplastic cells showed rhabdoid features or vacuolated cytoplasm. Immunohistochemically, the neoplastic cells were positive for vimentin and S100 and partly positive for neuron-specific enolase and glial fibrillary acidic protein but were negative for von Willebrand factor, desmin and α-smooth muscle actin. Ultrastructurally, the neoplastic cells had abundant cytoplasmic processes and desmosome-like structures. Cytoplasmic inclusions of rhabdoid-featured cells in HE sections were composed of aggregates of intermediate filaments, and cytoplasmic vacuoles were identified as an invagination of cytoplasm. Although malignant peripheral nerve sheath tumor was suggested according to these results, the present case was diagnosed as a soft tissue sarcoma with rhabdoid features due to a lack of identification of the basal lamina under electron microscopy.

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          Prognostic factors for cutaneous and subcutaneous soft tissue sarcomas in dogs.

          Soft tissue sarcomas (STSs) develop from mesenchymal cells of soft tissues, and they commonly occur in the skin and subcutis of the dog. Although phenotypically diverse with frequently controversial histogenesis, STSs are considered as a group because they have similar features microscopically and clinically. Following resection, local recurrence rates are low in general but vary according to histologic grade and completeness of surgical margins. Complete margins predict nonrecurrence. Even most grade I STSs with "close" margins will not recur, but propensity for recurrence increases with grade. The frequency of metastasis has not been accurately estimated, but it is believed to be rare for grade I STSs and most likely to occur with grade III STSs. However, metastasis does not necessarily equate with poor survival. High mitotic index is prognostic for reduced survival time. Further research is needed to determine more precise estimates for recurrence rates and survival as related to completeness of surgical margins and to delineate potential differences in metastatic rate and median survival time between grades. Other potential indicators of prognosis that presently require further investigation include histologic type, tumor dimension, location, invasiveness, stage, markers of cellular proliferation, and cytogenetic profiles. Common issues limiting prognostic factor evaluation include biases from retrospective studies, small sample sizes, poor verification of metastasis, inconsistent STS classification and use of nomenclature, difficulties in differentiating STS phenotype, and diversity of the study population (stage of disease and treatment status).
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            Immunohistochemical evaluation of canine peripheral nerve sheath tumors and other soft tissue sarcomas.

            Seventeen cases of canine peripheral nerve sheath tumors (PNSTs), 11 malignant PNSTs (MPNSTs), and six benign PNSTs (BPNSTs) were examined. The prognosis in five of six dogs with BPNSTs was excellent, whereas all dogs with MPNSTs died within 2 years after the last surgical resection. One BPNST formed a recurrent mass with features of a MPNST. Histopathologically, the predominant tumor cell of MPNSTs was either spindle or round in shape with epithelioid characteristics. Other atypical cells had abundant granular cytoplasm or were multinucleated giant cells with periodic acid-Schiff-positive cytoplasmic globules. Furthermore, two MPNSTs contained cartilaginous and osseous metaplasia. On the contrary, most BPNSTs exhibited typical features of schwannoma or neurofibroma, whereas two BPNSTs had atypical morphology. One BPNST consisted of epithelioid cell proliferation with some tumor cells revealing nuclear atypia. Immunohistochemically, the expression of vimentin (100%), S-100 (73%), nerve growth factor receptor (NGFR, 64%), and myoglobin (64%) was commonly found in MPNSTs. The two BPNSTs with atypical histologic appearances were positive for vimentin, S-100, NGFR, and neuron-specific enolase, and one of these had moderate immunoreactivity for cytokeratin. Most BPNSTs were positive for glial fibrillary acidic protein, as well as S-100 and NGFR. Although most rhabdomyosarcomas (RMSs) and canine hemangiopericytomas (CHPs) also showed focal immunoreactivity for S-100, most RMSs were intensely positive for myoglobin and negative for NGFR. Most CHPs (80%) exhibited focal alpha-smooth muscle actin (alpha-SMA) expression, whereas all PNSTs were negative. These results indicate that immunohistochemistry for NGFR and alpha-SMA might be useful for differentiating canine PNSTs from RMSs or CHPs, respectively.
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              Epithelioid variant of malignant peripheral nerve sheath tumor (malignant epithelioid schwannoma).

              Twenty-six cases of malignant peripheral nerve sheath tumor with a predominant epithelioid pattern were studied to determine the range of its histologic patterns, immunophenotype, and biologic behavior. The tumor presented as an asymptomatic mass either in superficial (16 cases) or in deep soft tissue (10 cases) of the extremity. Characteristically, those in deep soft tissue were composed of vague nodules of varying cellularity made up of cords or strands of rounded epithelioid cells with prominent nucleoli. Those in superficial soft tissue were uninodular masses composed of tight clusters of cells showing cell-to-cell molding but possessing the same prominence of nuclei and mitotic activity as those in deep soft tissue. Several were associated with a preexisting benign nerve sheath tumor. A number of cases deviated from the above description, including cases that resembled a clear cell carcinoma, a malignant rhabdoid tumor, and a pleomorphic sarcoma. The majority of cases (80%) strongly expressed S-100 protein and neuron-specific enolase, but all lacked a melanoma-associated antigen (as defined by HMB-45) and cytokeratin. Stains for type IV collagen defined linear immunoreactivity around single cells and groups of cells. This pattern did not differ substantially from that of melanomas and therefore did not serve as a reliable discriminant. Follow-up information indicated a more favorable course for those in superficial soft tissue compared with those in deep sites. Two of 16 patients in the former group developed metastatic disease compared with three of 10 in the latter group. Tumors in superficial soft tissue may be eminently treatable and curable, depending on size.

                Author and article information

                J Toxicol Pathol
                J Toxicol Pathol
                Journal of Toxicologic Pathology
                Japanese Society of Toxicologic Pathology
                05 February 2014
                July 2014
                : 27
                : 2
                : 131-138
                [1 ] Medicinal Safety Research Laboratories, Daiichi Sankyo Co., Ltd., 16-13 Kita-Kasai 1-Chome, Edogawa-ku, Tokyo 134-8630, Japan
                [2 ] Biological Research Department, Daiichi Sankyo RD Novare Co., Ltd., 16-13 Kita-Kasai 1-Chome, Edogawa-ku, Tokyo 134-8630, Japan
                Author notes
                *Corresponding author: A Sayama (e-mail: sayama.ayako.wh@ 123456daiichisankyo.co.jp )
                ©2014 The Japanese Society of Toxicologic Pathology

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (by-nc-nd) License.

                : 09 August 2013
                : 04 January 2014
                Case Report

                canine,soft tissue sarcoma,peripheral nerve sheath tumor,canine hemangiopericytoma,rhabdoid features


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