Low expression of p27^kip1, a cyclin-dependent kinase inhibitor, is a marker of poor prognosis in synovial sarcoma

BACKGROUND. Low expression of p27^kip1, a dominant cyclin-dependent kinase inhibitor involved in G1-S transition of the cell cycle, recently has been reported to be associated with aggressive tumor growth. It has been shown that active cell proliferation alludes to poor prognosis in patients with synovial sarcoma. However, to the authors knowledge, little is known about the clinicopathologic significance of p27^kip1 in synovial sarcoma. METHODS. p27^kip1 expression was examined immunohistochemically in 55 cases of primary synovial sarcoma, and the relations between p27^kip1 expression and several cell proliferation markers, i.e., mitotic index (MI), Ki-67 labeling index (Ki-67 LI), and clinicopathologic parameters related to poor prognosis, were determined. Univariate and multivariate survival analyses were performed to evaluate the prognostic significance of p27^kip1 expression in synovial sarcomas. RESULTS. p27^kip1 labeling index (p27^kip1 LI) correlated inversely with MI (r = -0.44, P = 0.0007) and Ki-67 LI (r = -0.63, P < 0.0001). Of the clinicopathologic parameters examined, tumor necrosis (P = 0.019) and American Joint Committee on Cancer (AJCC) stage (P = 0.021) correlated significantly with p27^kip1 LI. Survival analysis showed that p27^kip1 LI was an independent prognostic factor for overall survival in patients with synovial sarcoma (P = 0.0031). CONCLUSIONS. The study results suggested that low expression of p27^kip1 may be useful as a marker of poor-prognosis synovial sarcoma.