Gastric cancer is the fourth most common cancer worldwide. Although it is important to identify patients at high risk for a poor outcome, factors correlating with prognosis in gastric cancer are largely unknown. Here, we focus on the correlations among expression of Polo-like kinase 1 (PLK1), DNA ploidy, and clinical outcome in gastric cancer patients. Gastric cancer specimens were analyzed from 207 consecutive patients. Patients were classified into two groups according to tumor PLK1 expression and DNA content, and an analysis of their clinical outcomes was carried out. Prognoses of patients with PLK1-high tumors were worse than those of patients with PLK1-low tumors, but the differences were not statistically significant. In cell lines, overexpression of PLK1 induced centrosome amplification and multipolar spindles, potentially leading to DNA aneuploidy. Indeed, high expression of PLK1 was also associated with DNA aneuploidy in clinical gastric cancer specimens. Patients with both high PLK1 expression and DNA aneuploidy had poor recurrencefree survival, whereas PLK1 expression and DNA ploidy status alone were not significantly associated with outcome. Here, we provide clinical evidence that high expression of PLK1 could have detrimental effects in tumors with DNA aneuploidy, which may increase the risk of recurrence in gastric cancer patients.
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