Objects: CDX2 is a widely used immunohistochemical marker for intestinal differentiation in neoplasms. In the Nordic Immunohistochemical Quality Control external quality assessment scheme, only 45% of the laboratories participating in the CDX2 challenge in 2009 produced sufficient staining. A major cause of insufficient staining results appeared to be less successful primary antibody (Ab) clones. To evaluate the Ab performance in a standardized way, a comparative study was carried out.
Materials and methods: Tissue microarrays containing 309 non-neoplastic tissues and tumor samples with expected high, low, and no CDX2 expression were used. Five Abs were selected for comparison: EPR2764Y concentrated (Conc), EPR2764Y in a ready-to-use format, and DAK-CDX2, AMT28, and CDX2-88, all Conc. The CDX2 stains were scored blindly using the H-score method. Tissue/tumor samples with a maximum H-score of 150 to 300 (on the basis of the staining giving the highest score) were classified as CDX2 high expressors, samples with a maximum H-score of 10 to 149 as low expressors, and samples with a maximum H-score <10 as negative.
Results and conclusions: A total of 106 tumors were CDX2 positive with at least one of the Abs. For 56 high-expressor tumors, the mean H-scores with EPR2764Y Conc, EPR2764Y ready-to-use, DAK-CDX2, AMT28, and CDX2-88 were 262, 236, 234, 167, and 149, respectively, and the percentage of positive tumors 100, 100, 100, 98, and 93, respectively. For 50 low-expressor tumors, the mean H-scores with the same Abs were 59, 26, 28, 7, and 5, respectively, and the percentage of positive tumors 98, 58, 64, 18, and 14, respectively. With EPR2764Y Conc, CDX2 was demonstrated in 5/19 (26%) urothelial carcinomas, 7/64 (11%) lung adenocarcinomas, 5/30 (17%) large cell/sarcomatoid lung carcinomas, and 4/19 (21%) esophagus squamous cell carcinomas. In-house optimized protocols gave for all 4 Conc Abs better staining results than the vendors' recommended protocols. The sensitivity of CDX2 Abs and protocols must be taken into consideration when classifying neoplasms of unknown origin.