Prognostic significance of carbonic anhydrase IX expression by cancer-associated fibroblasts in lung adenocarcinoma

BACKGROUND: Cancer tissue is comprised of cancer cells and several types of stromal cells, including cancer-associated fibroblasts (CAFs). Carbonic anhydrase (CA) IX has been used as an endogenous hypoxia marker, and although its expression by cancer cells has been reported to be associated with a poor outcome in a board range of tumors, to the authors' knowledge, the biologic significance of its expression by CAFs remains unclear. METHODS: The authors investigated CA IX expression by CAFs and cancer cells immunohistochemically in 158 consecutive resected cases of lung adenocarcinoma. RESULTS: CA IX was expressed by CAFs in 39 (24.7%) of the 158 cases and by cancer cells in 40 (25.3%) cases. CA IX expression by CAFs was found to be significantly correlated with conventional prognostic factors, including pathologic tumor classification and lymph node involvement. A univariate analysis and the log-rank test demonstrated a significant association between CA IX expression by CAFs (P = .006 and P = .0052, respectively) and by cancer cells (P = .020 and P = .0179, respectively) with lower survival rate. A multivariate analysis of these 2 factors indicated a statistically significant association between CA IX expression by CAFs and a lower survival rate (hazards ratio [HR], 1.797; P = .032), but not between expression by cancer cells and lower survival rate (HR, 1.561; P = .102). CONCLUSIONS: The findings of the current study indicate that CA IX expression by CAFs was a better predictor of outcome than CA IX expression by cancer cells and provides new insights into the biologic significance of CAFs in the hypoxic microenvironment of the lung adenocarcinoma.