A33 shows similar sensitivity to but is more specific than CDX2 as an immunomarker of colorectal carcinoma.

AIMS:CDX2 is widely used as a sensitive and specific immunomarker for colorectal carcinoma (CRC), but neither its sensitivity nor its specificity is absolute. The aim of this study was to compare CDX1 and A33 with CDX2 as immunomarkers for CRC. METHODS AND RESULTS:As a pilot study, whole sections of 51 cases of liver metastatic carcinoma with different origins-colorectum (n = 32), breast (n = 3), oesophagogastric tract (n = 4), lung (n = 3), pancreas (n = 8), and prostate (n = 1)-were immunostained with CDX1, CDX2, and A33. A33 showed higher sensitivity as a CRC immunomarker, greater interobserver reproducibility for assessment of expression and less background cross-reactivity than CDX1. Therefore, only A33 was compared with CDX2 for a tissue microarray (TMA)-based study of primary adenocarcinomas with different origins: CRC (n = 55), liver deposits of metastatic CRC (n = 60), breast (n = 101), lung (n = 40), oesophagogastric tract (n = 134), ovary (n = 67), pancreas (n = 77), and prostate (n = 56). When the whole section and TMA cases of CRC were combined, A33 had a sensitivity of 95.9% and CDX2 had a sensitivity of 97.2%. When the whole section and TMA cases of non-colorectal carcinomas were combined, A33 had a specificity of 85.4% as a marker of CRC and CDX2 had a specificity of 64.3%. The higher specificity of A33 than of CDX2 as a CRC immunomarker was particularly seen among pancreatic and ovarian carcinomas. Furthermore, unlike what was seen with CDX2, none of the prostatic and lung carcinomas studied showed A33 positivity. CONCLUSIONS:A33 shows similar sensitivity to but is more specific than CDX2 as an immunomarker of CRC.

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