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. 2014 Aug;45(8):1704-12.
doi: 10.1016/j.humpath.2014.04.008. Epub 2014 Apr 24.

BRAF-mutated microsatellite stable colorectal carcinoma: an aggressive adenocarcinoma with reduced CDX2 and increased cytokeratin 7 immunohistochemical expression

Michael S Landau  1 , Shih-Fan Kuan  1 , Simon Chiosea  1 , Reetesh K Pai  2
Affiliations

BRAF-mutated microsatellite stable colorectal carcinoma: an aggressive adenocarcinoma with reduced CDX2 and increased cytokeratin 7 immunohistochemical expression

Michael S Landau et al. Hum Pathol. 2014 Aug.

Abstract

Reduced CDX2 and cytokeratin 20 (CK20) expression in colorectal carcinoma with BRAF mutation and high-level microsatellite instability (MSI-H) has been well documented. The immunophenotype of BRAF-mutated microsatellite stable (MSS) colorectal carcinoma has not been reported. We analyzed 205 colorectal carcinomas including 28 BRAF-mutated MSS, 53 BRAF-mutated MSI-H, and 124 BRAF wild-type MSS tumors for CDX2, cytokeratin 7 (CK7), and CK20 immunohistochemical expression. CDX2 was scored semiquantitatively for both staining intensity and percent of tumor cells staining and a modified CDX2 H-score was calculated. Patients with BRAF-mutated MSS colorectal carcinomas were more frequently stage IV at presentation compared to patients with BRAF-mutated MSI-H colorectal carcinomas and BRAF wild-type MSS colorectal carcinomas (32% versus 8% versus 15%, P < .001). BRAF-mutated MSS colorectal carcinoma displayed reduced CDX2 expression compared to BRAF wild-type MSS colorectal carcinoma (75% versus 94%; mean CDX2 H-score 98 versus 150, P < .001). CK7 expression was more often identified in BRAF-mutated MSS colorectal carcinoma compared to both BRAF-mutated MSI-H colorectal carcinoma and BRAF wild-type MSS colorectal carcinoma (39% versus 6% versus 6%, P = .0001). BRAF-mutated MSI-H colorectal carcinomas were less often CK20 positive compared to BRAF-mutated MSS and BRAF wild-type MSS tumors (70% versus 93% versus 90%, P = 0.001). In summary, BRAF-mutated MSS colorectal carcinoma often displays reduced CDX2 and increased CK7 expression. Knowledge of this altered immunophenotype is important as patients with BRAF-mutated MSS colorectal carcinoma often present with metastatic disease and the altered tumor immunophenotype may lead to the erroneous assumption that origin from the colon/rectum is unlikely.

Keywords: BRAF; CDX2; CK7; Colorectal carcinoma; Immunohistochemistry; MSI.

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