Overexpression of p53 and rare genetic mutation in mesenchymal chondrosarcoma.

Mesenchymal chondrosarcoma is extremely rare and accounts for less than 2% of all chondrosarcomas. The pathogenesis and the molecular genetic events which contribute to the development of mesenchymal chondrosarcoma are not well elucidated, due in part to the lack of sufficient tumor tissue available. To characterize the involvement of the p53 gene abnormality in this disease, we analyzed expression and sequence alteration of p53 by immunohistochemical analysis of the protein expression and quantitative DNA/PCR and PCR-SSCP assays of the gene in 33 paraffin-embedded tissue specimens. Immunohistochemical analysis demonstrated that 19 (61.3%) of 31 had nuclear overexpression of p53 while 7 (22.6%) showed cytoplasmic expression. The remaining 5 (16.1%) were negative for p53 staining. The nuclear positivity of p53 was observed within a range of 22-64% (mean 37.3%) of tumor cells and showed a positive staining in mesenchymal components as well as chondroid components. Quantitative DNA/PCR analysis revealed that 6 (18.2%) of the 33 specimens carried significantly reduced or undetectably low levels of p53 indicating the genomic deletion of the gene in these tumors. In contrast, however, DNA/PCR-SSCP analysis failed to detect any types of mutations resulting in amino acid substitution within exons 5-9 regions of the gene. Taken together, our data suggests that genetic alteration of p53 is a relatively rare event in mesenchymal chondrosarcomas but substantial fraction of this type of tumors carries abnormal overexpression of p53, which might result from as yet unidentified epigenetic mechanism(s).

Kasabach-Merritt syndrome: identification of platelet trapping in a tufted angioma by immunohistochemistry technique using monoclonal antibody to CD61.

Kasabach-Merritt syndrome (KMS) consists of large and rapidly growing vascular tumors associated with thrombocytopenia, generalized petechiae, and bleeding. The cause of the thrombocytopenia is thought to be related to the trapping of platelets by the abnormal endothelium of the tumor. We report an infant with KMS that developed in association with a large tufted angioma. In this case we directly demonstrated platelet trapping in the vascular lumen of the tumor by an immunohistochemical technique using a monoclonal antibody against CD61, a marker of platelets and megakaryocytes.

Pseudoanaplastic chondromyxoid fibroma.

A 19-year-old man presented with a chondromyxoid fibroma of the distal phalanx of the great toe that was originally diagnosed as osteosarcoma rather than "dedifferentiated" chondrosarcoma. Radiographs showed a large, expansive, and calcified tumor of the distal phalanx. Although the tumor had the architectural and matrix patterns of a chondromyxoid fibroma, high-power examination demonstrated that the lesion had such severe nuclear pleomorphism that it was mistaken for high-grade sarcoma. The purpose of this report is to present the criteria used to differentiate a benign pseudoanaplastic chondromyxoid fibroma from chondrogenic high-grade sarcomas.