p12 CDK2-associating protein 1 (p12CDK2-AP1) is a growth suppressor that negatively regulates cyclin-dependent kinase 2 (CDK2) activities. In addition, p12CDK2-AP1 has also been shown to interfere in DNA replication. A reduction of p12CDK2-AP1 expression is known to be a negative prognostic indicator in patients with oral squamous cell carcinoma. To elucidate the role of p12CDK2-AP1 expression in esophageal squamous cell carcinoma (ESCC), we immunohistochemically examined the expression of p12CDK2-AP1 protein in 120 resected ESCC specimens and determined its association with the clinicopathological characteristics and prognosis. Of the 120 ESCCs, 79 (65.8%) showed positive staining (≥25% of cancer cells showing p12CDK2-AP1 expression), while 41 (34.2%) lacked the staining (<25% of cancer cells showing p12CDK2-AP1 expression). Negative staining for p12CDK2-AP1 was found to be significantly associated with advanced lesions [depth of tumor (P=0.001), lymph node metastasis (P<0.001), pathological stage (P<0.0001) and venous invasion (P<0.0001)], and a poor prognosis (disease-free survival and overall survival: log-rank P<0.05). The rate of lymph node metastasis in patients with p12CDK2-AP1 negative-T1 ESCC was significantly higher than that in patients with p12CDK2-AP1 positive one (P<0.05). These results suggest the down-regulation of p12CDK2-AP1 to be related to tumor aggressiveness and a poor prognosis in patients with ESCC.

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