Clinicopathological features of follicular variant of papillary thyroid carcinoma
Reviewed by Shabbir Akhtar

The follicular variant (FV) of papillary thyroid carcinoma (PTC) is characterised by the presence of nuclear features of PTC together with a follicular growth pattern. It is currently reported to make up 11.8% to 53.3% of all PTC cases. It has a different genetic profile, with a lower prevalence of BRAF mutations and a higher incidence of RAS mutation, similar to follicular adenoma and follicular carcinoma. The purpose of the present study was to compare the clinicopathologic features of conventional papillary thyroid carcinoma and follicular variant of PTC and to see if major difference in prognosis is present. Conventional PTC was significantly more likely than FV PTC to have a malignant cytologic diagnosis. In contrast, FV PTC was significantly more likely to have false-negative benign preoperative cytologic findings. The mean size of the tumor in FV PTC was significantly greater than that of conventional PTC. There was a significant difference in incidence of microscopic extrathyroid extension (ETE). All cases of grossly invasive carcinoma occurred in the conventional PTC group. This study found some important differences in relation to preoperative cytologic findings, mean tumor size at diagnosis and incidence of ETE; but not in patient age or sex, incidence of tumour multicentricity or bilaterality, incidence of lymph nodes metastases, or prognostic grouping. Aspirates from cases of FV PTC are more likely to have had a false-negative (benign) cytologic result. This is an important issue because cases belonging to low-risk cytologic categories may be more likely to be recommended for nonsurgical follow-up, which may lead to increased risk of delayed diagnosis or failure to diagnose cases of FV PTC. 

Follicular variant of papillary thyroid carcinoma: differences from conventional disease in cytologic findings and high-risk features.
Sheahan P, Mohamed M, Ryan C, Feeley L, Fitzgerald B, McCarthy J, Tuthill A, Murphy MS.
JAMA OTOLARYNGOL HEAD NECK SURG
2014;140(12):1117-23.