PPARγ Staining as a Surrogate for PAX8/PPARγ Fusion Oncogene Expression in Follicular Neoplasms: Clinicopathological Correlation and Histopathological Diagnostic Value

The PAX8/PPARγ (PPFP) fusion-oncogene is moderately specific for follicular thyroid carcinomas (FTC). It remains unknown whether this can be translated into improved diagnosis, classification, or outcome prediction. We studied a cohort of well-characterized follicular adenomas (FA), FTC, and Hurthle cell carcinomas (HCC) from patients with complete clinical follow-up, to determine whether PPARγ immunohistochemistry (as a surrogate of PAX8/PPARγ expression) helps to distinguish FA from FTC and to assess its diagnostic accuracy as an adjunct to frozen section. We also correlated PPARγ staining with clinical outcomes to assess its role as a prognostic marker. PPARγ staining was more common in FTC (31 of 54; 57%) than in HCC (one of 23; 4%) or FA (four of 31; 13%) (P < 0.000001). Adjunctive use of PPARγ immunohistochemistry improved diagnostic sensitivity of intraoperative frozen section from 84% to 96% (P < 0.05) but reduced specificity from 100% to 90% (P < 0.05). PPARγ staining was associated with favorabl...