Cribriform Morular Thyroid Carcinoma With <scp> <i>CTNNB1</i> </scp> Mutation: Report of One Unique Case and Review of the Literature

Cribriform Morular Thyroid Carcinoma (CM-TC) is a rare thyroid malignancy characterized by distinctive histomorphologic and genetic features, primarily driven by continuous activation of the WNT/β-catenin signaling pathway. However, diagnosis can be challenging on fine needle aspiration biopsy due to its rarity and overlapping cytomorphologic features with other thyroid tumors. We present a unique case of CM-TC displaying long papillary fronds and intracytoplasmic globules, reminiscent of solid pseudopapillary tumor of the pancreas. These two cytologic features have not been previously described in the literature. Molecular analysis (ThyroSeq) revealed an activating CTNNB1 (beta-catenin) exon 3 mutation in this case, which is also commonly observed in solid pseudopapillary tumors of the pancreas. We propose that morphologic similarity may be a consequence of a similar mutation. Recognizing these novel characteristics may aid in distinguishing CM-TC from other thyroid tumors, improving diagnostic accuracy and patient management.