Calcifying/ossifying synovial sarcoma shows t(X;18) with SSX2 involvement and mitochondrial calcifications

Aims: Synovial sarcoma with extensive calcification and ossification is a r are variant, the ultrastructural, cytogenetic and molecular analysis of whi ch has not been reported previously. Methods and results: A large mass in the shoulder of a 20-year-old male pat ient led to a deformity of the chest wall, thus supporting the hypothesis t hat this is a slowly growing variant of synovial sarcoma, Nevertheless, the patient developed metastatic lung disease 7 months after resection. On his tology, the monophasic spindle cell proliferation was in several areas obsc ured by the massive calcification and ossification. Immunohistochemistry sh owed keratin, epithelial membrane antigen, vimentin and CD99 expression. Th e cytogenetic analysis revealed a single t(X;18)(p11.2: q11.2), typical for synovial sarcoma. Additional fluorescence in-situ hybridization revealed S SX2 involvement. At the ultrastructural level, prominent needle-shaped intr amitochondrial crystals were present, both in the cytoplasm and in the extr acellular matrix. Conclusion: The presence of the t(X:18) with SSX2 involvement definitively characterizes this tumour as a variant of synovial sarcoma. In addition, th e needle-like mitochondrial calcifications give a possible clue to the path ogenesis of the extensive metaplastic ossification and calcification.