New Neuroendocrine Markers PITX2, PHOX2B, and HAND2 Do Not Offer Diagnostic Utility in Fine-needle Aspiration Biopsies of Primary and Secondary Medullary Thyroid Carcinomas: A Retrospective Multi-institutional Study

Medullary thyroid carcinoma (MTC) is a neuroendocrine malignancy arising from parafollicular C-cells with known variations in cytomorphologic and immunophenotypic features. New neuroendocrine markers pituitary homeobox 2 (PITX2), paired-like homeobox 2B (PHOX2B), and heart and neural crest derivatives expressed 2 (HAND2) have recently been introduced, but studies using these markers in MTC are limited. The aim of this study was to evaluate the expression and potential diagnostic utility of PITX2, PHOX2B, and HAND2 in primary and secondary MTCs and to compare their expression with chromogranin A, synaptophysin, insulinoma-associated protein 1 (INSM1), and calcitonin.