Differential diagnostic and functional role of the multi-marker phenotype CDX2/CK20/CK7 in colorectal cancer stratified by mismatch repair status.

The differentiation of colorectal cancer from primary tumors at other sites can be challenging. Often a panel of immunohistochemical protein markers is needed to distinguish between these entities. Protein expression differs significantly in colorectal cancer depending on mismatch repair status and is also heterogeneous among mismatch repair-proficient or -deficient tumors. The aim of this study was to systematically analyze the diagnostic and prognostic role of the commonly used multi-marker phenotype CK20/CK7/CDX2 on a large series of colorectal cancers stratified by mismatch repair status. The immunohistochemical analysis of CK20, CK7 and CDX2 was performed on 1197 mismatch repair-proficient and 223 mismatch repair-deficient colorectal cancers using a tissue microarray. Multi-marker combinations of CK20/CK7/CDX2 were explored. Univariate and multivariable analysis of the markers was evaluated for their association with several clinico-pathological end points namely T stage, N stage, tumor grade, vascular invasion, intratumoral lymphocytes and survival. Multi-marker phenotypes with CK20 and CDX2 negativity were more frequently found in mismatch repair-deficient than in mismatch repair-proficient colorectal cancer (19.3 vs 7.5% and 21.6 vs 6.7%, respectively; P<0.001). In both colorectal cancer subsets loss of CK20 was associated with higher tumor grade (P<0.001) and with presence of intratumoral lymphocytes (P<0.001 and P=0.02, respectively). In the proficient mismatch repair subset CK20 overexpression was an independent adverse prognostic factor (P=0.041) and CDX2 underexpression was linked to tumor progression. Loss of CDX2 and CK20 is more frequently encountered in mismatch repair-deficient colorectal cancer, which should be taken into consideration to differentiate between primary and metastatic colorectal cancer in daily practice. Although associated with lower tumor grade, CK20 overexpression is an independent adverse prognostic factor in mismatch repair-proficient colorectal cancer.