Sarcomatoid adenocarcinoma of the lung: clinicopathological, immunohistochemical and molecular analyses.

Background: Biphasic lung cancers with admixtures of adenocarcinoma and sarcornatoid components but lacking true mesenchymal differentiation (sarcomatoid adenocarcinomas) are rare, and extensive studies of their clinicopathological characteristics and histogenesis have not been performed. Materials and Methods: Six surgically resected sarcomatoid adenocarcinomas were compared clinicopathologically with 317 standard adenocarcinomas, and studied immunohistochemically and by loss of heterozsgosity (LOH) analysis focusing on each component. Results: In comparison with standard adenocarcinomas, the sarcomatoid adenocarcinomas occurred in older patients, were more likely to be associated with smoking and were more acinar than papillary, with a worse five-year prognosis. Immunohistochemically, sarcomatoid components were positive for epithelial markers in three cases. In one case the carcinoma showed retention of heterozygosity and the sarcomatoid components allelic loss, while all other cases showed retention or LOH in both components. Conclusion: The sarcomatoid adenocarcinoma exhibits different clinicopathological characteristics from standard adenocarcinomas. The present immunohistochemical and LOH analyses provided support for the idea that both components are derived from one precursor cell, and that progression may be by way of adenocarcinoma to sarcomatoid differentiation.