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There is no optimal established therapy for treating advanced or recurrent adenocarcinoma with bronchioloalveolar carcinoma features (ADC-BAC), and it remains unclear whether chemotherapy achieves therapeutic results comparable to those seen in the more common non-small lung carcinoma subtypes. In order to improve the decisions made during the treatment of advanced ADC-BAC, we attempted to better characterize the mucinous and non-mucinous ADC-BAC subtypes. Fifty pathological samples were obtained from 62 patients included in a multicenter prospective phase II trial (IFCT0401) conducted to evaluate gefitinib as a first-line therapy for non-resectable ADC-BAC. These samples were centrally reviewed and re-classified as non-mucinous (n=25) or mucinous (n=25) subtypes. We demonstrated that demographic data, clinical characteristics and stage at presentation (extrathoracic versus lung metastasis, as well as TNM staging) did not distinguish between the two subtypes. In contrast, three biological markers (PAS staining, TTF-1 expression and EGFR genomic gain combined with mutation analysis) enabled us to independently segregate all but 2 of the 50 patients into the mucinous and non-mucinous ADC-BAC subtypes. Finally, only mucinous tumors appeared to be resistant to epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs). Additional prospective studies are required to better approach therapeutic strategy in mucinous tumors, which are a distinct entity from non-mucinous tumors.