Impact of expert review of histological diagnosis of papillary and follicular thyroid cancer

Purpose: Histologic and pTNM classification of differentiated thyroid cancer (DTC) is mandatory to assess risk of relapse, risk of death, and radioactive iodine administration. The impact of an expert central review of external pathology reports has not yet been reported. Methods: Monocentric retrospective study to evaluate the difference between initial and second-opinion histopathologic diagnosis for DTC patients referred for post-operative radioactive iodine administration between January 2014 and December 2016. We evaluated major discordance (change of diagnosis from malignant to benign or in main histological subtype or a description of aggressive pathological subtypes), minor discordance (change in histological subtype or description of an aggressive component, multifocality or extrathyroidal extension), and change in ATA classification. Results: A second-opinion histological diagnosis was available for 199 patients. A major discordance was observed in 42 (21%) cases (changes in malignancy in 4 cases, changes in main histological subtype in 22, changes in aggressive pathology variants of PTC in 16). One hundred and four minor discordances were observed regarding 92 patients. These histopathological changes led to changes in the ATA 2015 risk stratification classification in 61 (31%) of cases. There were no predictive factors of major/minor histologic changes or ATA risk stratification changes. Conclusion: Expert central review of pathology has an impact on the 2015 ATA risk stratification classification that can lead to changes in the management of patients with differentiated thyroid cancer.