Decreased expression of speckle-type POZ protein for the prediction of poor prognosis in patients with non-small cell lung cancer

Speckle-type POZ domain protein (SPOP) has been acknowledged as a tumor suppressor gene in numerous types of cancer. However, SPOP expression and its prognostic role in human non-small cell lung cancer (NSCLC) remain unknown. The present study investigated SPOP expression in NSCLC and evaluated its prognostic significance in patients with NSCLC. The results demonstrated that SPOP expression was significantly downregulated in NSCLC tissues at the mRNA and protein level compared with normal lung tissues using reverse transcription-quantitative polymerase chain reaction, and western blot analysis. Immunohistochemical staining results also demonstrated that SPOP was expressed at a low level in 84.1% (132/157) of NSCLC samples and at a high level in 52.2% (12/23) of normal lung samples, whereby the difference was statistically significant (P<0.001). In addition, it was revealed that the level of SPOP was associated with histologic type (P=0.003), tumor differentiation (P=0.046), tumor size (P=0.0036), lymph node metastasis (P=0.041) and clinical stages (P=0.046). Furthermore, the overall survival of patients with high SPOP expression was significantly increased compared with that of patients with low SPOP expression (P=0.003). These results revealed that SPOP expression was downregulated in NSCLC tissues and associated with poor prognosis in patients with NSCLC, suggesting that SPOP is an independent prognostic marker candidate for NSCLC.