SATB2 is a supplementary immunohistochemical marker to CDX2 in the diagnosis of colorectal carcinoma metastasis in an unknown primary.

CDX2 is routinely used for identifying gastrointestinal origin of metastatic adenocarcinomas; but a high percentage of other carcinomas also show positivity with this antibody. SATB2 is a new immunohistochemical marker with a few studies showing that it is specifically expressed in a large majority of colorectal adenocarcinomas. We assessed SATB2 along with CDX2 in patient material with metastasis in order to determine whether the primary site could be identified as 'colon-rectum'. Metastasis in 67 liver biopsies, 108 lymph nodes from resection specimens and 36 serous effusions was analyzed retrospectively. Blinded slides stained for CDX2 and SATB2 were assessed individually by two pathologists and sensitivity, specificity and kappa statistics were calculated. Sensitivity for CDX2 in metastasis from colorectal adenocarcinomas was 93%; while in SATB2 it was 79%. The combination of CDX2 and SATB2 yielded a sensitivity of 79% and a high specificity of 93%. There was an acceptable level of agreement (κ = 0.64) between the pathologists for both the markers in case of colorectal adenocarcinoma metastasis. CDX2 is a sensitive marker compared to SATB2; while the specificity of combination of CDX2 and SATB2 is high for metastasis from colorectal adenocarcinoma. SATB2 can be used as a supplementary marker along with CDX2 to identify colorectal origin for material received from patients clinically presenting with metastasis.