Background: Diffuse sclerosing variant (DSV) of papillary thyroid carcinoma (PTC) is a rare variant more common among younger patients. Materials and methods: Excluding patients with microcarcinoma, 5848 patients with PTC underwent initial surgery between 1995 and 2011. Twenty-two patients (0.4 %) were histologically diagnosed with DSV, of whom 20 (91 %) were <45 years old. We compared clinicopathologic characteristics and outcomes between patients with DSV and those with classical PTC <45 years old. Univariate analysis by the Kaplan-Meier method in relation to cause-specific survival (CSS) and disease-free survival (DFS) rates was performed with regard to the following variables: sex; anti-thyroglobulin antibody (TgAb) positivity; presence of distant metastasis; pathological lymph node metastasis; extra-thyroidal invasion; and pathological variant (classical vs. DSV). Results: The 20 patients with DSV <45 years old comprised 18 females and 2 males. Frequencies of TgAb, pN1b, and local recurrence were higher in the DSV group than in the classical PTC group. Ten-year CSS and DFS rates for PTC patients <45 years old were 99.7 and 88.6 % in the classical PTC group and 100 and 60.5 % in the DSV group. CSS rate did not differ between groups, but DFS rate was significantly lower in the DSV group than in the classical PTC group (p < 0.0001, log-rank test). Multivariate analysis identified DSV group and pN1b as prognostic factors for recurrence in young PTC patients. Conclusions: Most DSV patients were young and had a background of chronic thyroiditis. Outcomes for DSV were very good, but recurrence was more common than in classical PTC.
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