Braf mutation positive papillary thyroid carcinoma is less advanced when Hashimoto's thyroiditis lymphocytic infiltration is present.

Background Concomitant papillary thyroid cancer (PTC) and Hashimoto's thyroiditis (HT) is a frequent occurrence. Whether these two conditions are linked and whether PTC with concurrent HT has distinct clinicopathological characteristics are still debated issues. Lymphocytic infiltration is abundant in HT and might be relevant in the pathogenesis and progression of PTC. BRAFV600E mutation is associated with a more advanced PTC at diagnosis; however, its role in the clinicopathological characteristics of PTC with concurrent HT is unknown. Design and patients We enrolled 146 patients with histological diagnosis of PTC. Microscopic assessment of histology samples was performed to identify the presence of lymphocytic infiltration. Detection of BRAFV600E was performed on cytology samples by both direct sequencing and pyrosequencing, and results were correlated with clinical parameters. Results Concurrent HT lymphocytic infiltration was associated with the female gender, smaller tumour size, a less frequent extracapsular extension and a lower grade of TNM staging. BRAFV600E was more frequent in PTC with concomitant lymphocytic infiltration. In PTC harbouring BRAFV600E, concurrent lymphocytic infiltration was still associated with the female gender, a less frequent extracapsular extension and a lower TNM staging. Conclusions These results suggest that lymphocytic infiltration of HT is a protective factor against PTC progression, and it is independent of BRAF mutational status.