Papillary thyroid carcinoma is the most common type of thyroid malignancy. The 
diagnostic features of these tumors include characteristic nuclear cytology. 
However, many variants have been reported with different morphology and 
molecular profiles. Although the vast majority of papillary thyroid carcinomas 
have an excellent prognosis, some variants of papillary thyroid carcinoma can 
have a more aggressive course. With this increased attention to papillary 
thyroid carcinoma variants has come the need to sort out which variants are 
clinically important and should be recognized by practicing pathologists. The 
main objectives of this review article are to (1) summarize the gross and 
histopathologic features of papillary thyroid carcinoma; (2) provide an overview 
of the subtypes of papillary thyroid carcinoma and their prognosis; (3) discuss 
established and emerging data on the immunohistochemical findings that are 
helpful in differential diagnosis; and (4) summarize molecular findings and 
pathogenesis of these lesions.