Prevalence of a hobnail pattern in papillary, poorly differentiated, and anaplastic thyroid carcinoma: a possible manifestation of high-grade transformation.

Papillary thyroid carcinoma is the most common thyroid carcinoma and has a generally favorable prognosis. There are several well-characterized variants, some of which are associated with more aggressive clinical behavior. Hobnail is a recently described rare variant that appears to behave more aggressively.