Ki-67 labeling index affects tumor infiltration patterns of lung squamous cell carcinoma

Ki-67 is a nuclear protein that is expressed during the G(1), S, G(2) and M phases of the mitotic cell cycle. A previous study categorized tumor infiltration patterns (INF), of which INFc indicated cancer nests exhibiting infiltrative growth and an unclear boundary between tumor tissue and surrounding healthy tissue. The present study used the Ki-67 labeling index (Ki-67 LI) as an indicator of cell proliferation, in order to examine the factors affecting INF in lung squamous cell carcinoma (SqCC). SqCC specimens (89) were classified into two groups: High-grade cell proliferation (Ki-67 LI ≥30%) and low-grade cell proliferation (Ki-67 LI <30%). However, a high Ki-67 LI was significantly associated with cases that had an INFc component [INFc(+); P=0.03]. Univariate analyses indicated that INFc(+) was a predictor of venous invasion [P=0.032; odds ratio (OR), 2.615; 95% confidence interval (95% CI), 1.085–6.305], scirrhous stromal type (P<0.001; OR, 6.462; 95% CI, 2.483–16.817) and high Ki-67 LI (P=0.018; OR, 12.543; 95% CI, 1.531–102.777). Multivariate logistic analyses indicated that high Ki-67 LI was the strongest predictor of INFc(+) (P=0.028; OR, 8.027; 95% CI, 1.248–51.624). In conclusion, high-grade cell proliferation activity may contribute to aggressive infiltrative growth of lung SqCC.