Alterations of G1-S checkpoint in chordoma: the prognostic impact of p53 overexpression
To the authors' knowledge, little is known regarding the alterations of G(1)-S checkpoint and their significance in chordoma, a rare bone tumor. The authors investigated the clinicopathologic relevance of cell cycle abnormalities in chordoma. The expression levels of p53, murine double minute 2 (MDM2), retinoblastoma protein (pRb), cyclin D1, p16(INK4a), and p27(Kip1) were investigated using immunohistochemical techniques; p53 mutations were studied by polymerase chain reaction (PCR)-single-strand conformation polymorphism, and mdm2 amplification was analyzed using real-time quantitative PCR. The results were compared with clinicopathologic parameters in 101 lesions. Approximately 10-45% of primary tumors presented alterations of p53, MDM2, cyclin D1, and pRb proteins; most tumors lacked expression of p16(INK4a) and p27(Kip1). Alterations of p53, MDM2, cyclin D1, and pRb proteins were found to have cooperative effects on both higher proliferative ability (MIB-1 labeling index [LI]) and increased nuclear pleomorphism, a previously described prognostic indicator for patients with chordoma. Multivariate analyses revealed that, among these alterations, p53 overexpression was the only independent factor for higher MIB-1 LI. At the genetic level, mdm2 gene amplification was detected in 15.4% of the lesions but did not correlate with MDM2 overexpression or other clinicopathologic parameters. No p53 mutations were detected in the current series. Survival analysis revealed that p53 overexpression, but no other cell cycle alterations, was associated with a reduced overall survival. Accumulation of cell cycle alterations led to an increased MIB-1 LI and nuclear pleomorphism, a previously described prognostic indicator in chordoma. The authors believe that p53 overexpression in particular is associated with an unfavorable prognosis in patients with chordoma.