IQGAP1 is a scaffold protein whose function relates to signal transduction, cell adhesion, local invasion, and distant metastasis of cancer cells. We examined the expression patterns of this protein and clinicopathologic features of lung cancer, and the antibody against IQGAP1 was used for immunohistochemical analysis. Of the 70 surgical specimens examined, there were 40 adenocarcinomas, 19 squamous cell carcinomas, 5 large cell carcinomas, 3 small cell carcinomas, 2 carcinoid tumors, and 1 mucoepidermoid carcinoma. The localization of IQGAP1 was classified into three types: 1) cytoplasmic, 2) membranous, and 3) reduced expression. In adenocarcinoma, the 3 types were observed equally, and differentiation grade was related to the expression pattern. The cytoplasmic type was common in well-differentiated adenocarcinomas, and membranous or reduced expression was frequently seen in moderately- or poorly-differentiated adenocarcinomas. In squamous cell carcinoma, the membranous type was most common. Although the staining pattern of IQGAP1 did not correlate with the positivity of regional lymph nodes, survival in those patients with a cytoplasmic type was significantly better than others with adenocarcinoma (p=0.0144). Expression typing of IQGAP1 in lung cancer was associated with histologic type and can be used to predict survival in patients with adenocarcinoma of the lung.

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