Hashimoto's thyroiditis, nodular goiter or follicular adenoma combined with papillary thyroid carcinoma play protective role in patients.

Papillary thyroid carcinoma (PTC) is often combined with other types of thyroid disease, such as Hashimoto's thyroiditis(HT), nodular goiter(NG), Follicular adenoma(FA) and other types. However, the function of these diseases in PTC tumorigenesis and development is not well understood. In this research, 563 PTC patients were recruited and divided into two groups according to pathological diagnosis, namely simple PTC (PTC) and PTC combined with other thyroid diseases (PTC+). Clinicopathological characteristics and BRAFV600E mutation status were compared between PTC and PTC+. Our data showed that there was a statistically significant difference in gender (P=0.007), tumor diameter (5mm, P=0.012; 1cm, P=0.042), lymph node metastasis (P=0.000) and BRAFV600E mutation status (P=0.001) between PTC and PTC+. PTC+ patients have lower lymph node metastasis rate, even if PTC nodule diameter is larger than 5mm (P=0.005) or ≥1cm (P=0.049) or BRAFV600E is mutated (P=0.001). In conclusion, our study suggests that HT, NG and FA, are protective factors of PTC patients, and PTC+ patients have lower lymph node metastasis and BRAFV600E mutation rate compared with simple PTC patients.