Although distinguishing metastatic colorectal adenocarcinoma from primary lung adenocarcinoma is often difficult, pre- or intra-operative identification is very important, as the resection areas for each diagnosis differ substantially. CDX2, a recently cloned homeobox gene, represents a highly specific and sensitive marker of colorectal adenocarcinoma. We evaluated CDX2 expression using pre- and intra-operative biopsy specimens. The study examined 50 consecutive colorectal adenocarcinoma metastases to the lung, including 20 biopsy specimens and 66 resected specimens, and 21 primary lung adenocarcinomas. All specimens were immunohistochemically stained for CDX2, cytokeratin (CK) 7, CK20 and thyroid transcription factor (TTF)-1, and scored in a semi-quantitative manner. Mean staining score in biopsy specimens was significantly higher for CDX2 than for CK20. Sensitivities for CDX2 and CK7−/20+ in biopsy specimens were 95.0 and 65.0%, respectively. If CDX2 immunostaining had not been performed, 8 biopsy specimens (40%), and 20 resected specimens (30.3%) might have been diagnosed as equivocal cases either as primary lung cancer or metastatic colorectal cancer, using other markers. These results suggest that positive CDX2 staining represents a highly sensitive and specific marker of metastatic colorectal carcinoma in both biopsy and resected specimens, and is superior to staining for the CK7−/20+ phenotype.

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