We report a case of a 57-year-old male with anaplastic transformation of papillary thyroid carcinoma (PTC) in metastatic lymph nodes. This case presents as a pitfall due to squamous differentiation in anaplastic thyroid carcinoma, which was initially misinterpreted as metastatic squamous cell carcinoma on fine needle aspiration (FNA) of the lymph node in the neck. Subsequent surgical resection reveals a unique rare occurrence of isolated anaplastic transformation of tall cell PTC in the metastatic lymph nodes, associated with the extremely rare co-occurrence of BRAF p.V600E and KRAS p.G12R mutations.
Chia et al. (Tue,) studied this question.