Synovial sarcoma (SS) is a malignant soft tissue tumor characterized by its unique t(X;18)(p11;q11) chromosomal translocation leading to the formation of the SS18-SSX fusion gene. The resulting fusion protein product is considered to play as an aberrant transcription factor and transform target cells by perturbing their gene expression program. However, the cellular origin of SS is highly debated. We herein established two novel human SS cell lines, named Yamato-SS and Aska-SS, and investigated their biological properties. We found the self-renewal ability of these cells to generate sarcospheres, to form tumors in serial xenotransplantation and reconstitute the tumor phenotypes without fractionation by any surface markers. Both SS cells as well as clinical tissue specimens from 15 patients expressed the marker genes-associated stem cell identity, Oct3/4, Nanog, and Sox2. We also found that both SS cells displayed limited differentiation potentials for mesenchymal lineages into osteocytes and chondrocytes albeit with the expression of early mesenchymal and hematopoietic lineage genes. Upon SS18-SSX silencing with sequence-specific siRNAs, these SS cells exhibited morphological transition from spherical growth in suspension to adherent growth in monolayer, additional expression of later mesenchymal and hematopoietic lineage genes, and broader differentiation potentials into osteocytes, chondrocytes, adipocytes, and macrophages in appropriate differentiation cocktails. Collectively, these data suggest that a human multipotent mesenchymal stem cell can serve as a cell of origin for SS and SS is a stem cell malignancy resulting from dysregulation of self-renewal and differentiation capacities driven by SS18-SSX fusion protein.

Background. Angiosarcoma is rare, and information about its clinical features are limited. Therefore, a large scale study of angiosarcoma was performed in Japan. Methods. Through a nationwide Japanese study, 99 cases of angiosarcoma were collected and their clinicopathologic findings were summarized relative to predisposing risk factors. Results. The patient age at diagnosis was 3‐92 years, (mean, 62 years), with a two to one male to female ratio. The head and face were the most common primary site (29 cases); other sites were liver (17); trunk (13): pleural cavity (6), chest wall (2), abdominal wall (2), buttock (2), inguinal region (1); heart (12); and extremities (7). The proven predisposing risk factors included chronic pyothorax for angiosarcoma in the pleural cavity (six), thorotrast in the liver (five), radiotherapy to the abdominal wall and buttock (four), and chronic limb edema of the forearm (one). Irrespective of primary sites, the majority of cases had metastases to lung in 72 cases, bone in 42, liver in 36, regional lymph nodes in 30, and adrenal gland in 24. The 2‐year survival rate was 17.

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MRI shows features which were helpful for differentiating MPNST from NF.

Concentrated growth factor (CGF) is an autologous leukocyte-rich and platelet-rich fibrin (L-PRF) biomaterial termed "second-generation platelet concentrate". CGF contains autologous osteoinductive platelet growth factors and an osteoconductive fibrin matrix. The purpose of this study was to assess the ability of CGF combined with bone marrow stromal cells (BMSCs) to heal critical-size rat calvaria defects in vivo and to modulate the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) in vitro. In the in-vivo study, the CGF group regenerated bone better than the control group, and combined therapy with CGF and BMSCs almost completely repaired critical-size bone defects within 12 weeks after surgery. In the in-vitro study, the CGF extract, at concentrations between 1 and 10%, promoted proliferation, osteogenic maturation, and mineralization of hTERT-E6/E7 human MSCs in a dose-dependent manner but had an inhibitory effect at higher concentrations. In conclusion, a CGF extract promoted the proliferation, osteogenic maturation, and mineralization of mesenchymal stem cells in vitro, and combination therapy with CGF and BMSCs resulted in excellent healing of critical-size bone defects in vivo.