High prevalence of papillary thyroid carcinoma in nodular Hashimoto's thyroiditis at the first diagnosis and during the follow-up

Background The association between Hashimoto's thyroiditis (HT) and papillary thyroid carcinoma (PTC) remains to be elucidated. Materials and methods A total of 484 HT patients were retrospectively subdivided into two groups: 243 without thyroid nodules, TNs (HTN-) and 241 with TNs (HTN+). Fine-needle aspiration cytology was available in 152 HTN+ patients. This group was compared to a group of 161 patients with nodular goiter (NG) without HT. Finally, 70 HTN+ and 37 NG patients underwent surgery. Results A very high prevalence of suspicious/malignant cytology (Thy 4-5) at the first diagnosis (38/124; 31%) and during the follow-up (6/28; 22%) was found in HTN+ group. In HTN- group, 22/130 (17%) patients developed TN, but none showed malignant features during the follow-up. HTN+ patients had higher prevalence of Thy 4-5 (44/152 = 28.9%) compared to NG patients (12/161 = 7.4%, p < 0.0001). Increased independent odds ratio (OR) for malignancy was conferred by serum TSH > 1.0 mu UI/ml, [OR 1.93, 95% confidence interval (CI) 1.41-2.64, p < 0.0001], male sex (OR 3.44, CI 1.48-8.02, p = 0.004) and HT (OR 3.14; CI 1.08-9.31, p < 0.05). Malignant histology (mostly PTC) was confirmed higher in HTN+ (48/70, 68.6%) compared to NG (15/37, 40.5%; p < 0.05). Higher prevalence of extrathyroidal infiltration (24/48, 50%) and vascular invasion (25/48, 52%) was found in HTN+ vs NG (2/15, 1.3% p < 0.01), (3/16, 1.8% p < 0.05), respectively. Conclusions This study confirms higher prevalence of suspicious/malignant cytology and PTC at histology in nodular HT compared to NG, without evidence of malignancy in non-nodular HT patients during the follow-up.