Some reports have indicated that tumor MMP-9 expression is a prognostic factor for adenocarcinoma of the lung [11,24], and we analyzed that a higher proportion of the adenocarcinoma patients had positive tumor MMP-9 expression than squamous carcinoma in this study (28.0% vs. 61.5%; p = 0.001). The gene discussed is MMP9; the disease is squamous cell carcinoma.