Two Cases of Sinonasal Non-Intestinal-Type Adenocarcinoma with Squamoid Morules Expressing Nuclear β -Catenin and CDX2: A Curious Morphologic Finding Supported by Molecular Analysis.

Sinonasal non-intestinal-type adenocarcinoma (non-ITAC) is a rare, morphologically diverse neoplasm of the head and neck. Squamoid morular metaplasia has recently been reported as an occasional finding in non-ITAC. Interestingly, these squamoid morules often show aberrant expression of CDX2 as well as nuclear expression of β -catenin, similar to other tumors that show this type of metaplasia, but the underlying mechanism responsible for this finding is not completely understood. We present two cases of low-grade non-ITAC with squamoid morules coexpressing CDX2 and nuclear β -catenin by immunohistochemistry, both of which were found to harbor a mutation in CTNNB1 , the gene encoding β -catenin. This finding provides support that an alteration in the β -catenin pathway, including mutations in the β -catenin gene itself, is responsible for this recently described morphologic phenomenon in non-ITAC.