Proliferative activity of synovial sarcoma: an immunohistochemical evaluation of Ki-67 labeling indices of 52 primary and recurrent tumors.

The relationship between cell differentiation and proliferation in biphasic synovial sarcoma (BSS) and the connection between the two components of these tumors and monophasic synovial sarcoma (MSS) are still unknown. In this study we specifically compared the Ki-67 labeling indices (Ki-67-LI) in the solid/glandular and spindle cell components of primary BSS (n = 8) as well as the values thus obtained in primary BSS both outside clear-cut biphasic areas (n = 7) and in primary MSS (n = 23). We also compare the Ki-67-LI of primary tumors (seven BSS, seven MSS) and their respective first recurrences. We observed that the cells of the solid/glandular component of BSS proliferate significantly faster (p = 0.007) than those of spindle cell areas. No significantly different Ki-67-LI were observed in the comparison of the solid/glandular areas of BSS with the spindle/epithelioid component of BSS without clear-cut biphasia and MSS. No significant differences of Ki-67-LI were observed in the comparison of primary tumors of both subtypes with their respective first recurrences. The implications of the low proliferative activity of the spindle cell component of BSS exhibiting clear-cut biphasia, which was also confirmed in a concurrent study using anti-proliferating cell nuclear antigen/Cyclin PC10, remains to be clarified.