Columnar Cell Variant of Papillary Thyroid Carcinoma: A Study of 10 Cases with Emphasis on CDX2 Expression

Background: Columnar cell variant is a recognized rare variant of papillary thyroid carcinoma (PTC) that has an uncertain clinical course. This variant has two subvariants, and one is regarded as a more aggressive form in comparison to the more common classical and follicular variants. These tumors have morphological resemblance with endometrial or colonic adenocarcinoma. CDX2, a transcription factor of the caudal homeobox family, plays a key role in intestinal development and differentiation, and it is widely used as a marker to detect adenocarcinomas of intestinal and colonic origin. CDX2 has been rarely reported in PTC. Methods: We studied 10 cases of columnar cell variant of PTC (CCV-PTC). The histological, architectural, and cytological features fulfilled the diagnostic criteria of the CCV-PTC, as defined by the current World Health Organization classification. Ten patients (six men and four women) ranging in age from 32 to 90 years (mean, 58.3 years) presented with tumors classified as indolent (four cases) or aggressive (six cases); three harbored a BRAF V600E mutation. All cases were β-catenin negative. The Ki-67 proliferative index was up to 50%. All cases were thyroid transcription factor-1–positive. Using paraffin-embedded blocks, immunohistochemistry for CDX2 was performed to evaluate the reactivity of this antibody to this variant of PTC. Results: Nuclear positivity for CDX2 was detected in one out of the 10 cases studied (10%); the other nine cases did not express CDX2. Conclusion: Only one of our cases showed nuclear positivity for CDX2. Therefore, our study failed to confirm it as a marker for CCV-PTC. The absence of CDX2 in the majority of the cases does not support the theory of CDX2 playing a role in the intestinal phenotype of these tumors.