Higher prevalence of thyroid cancer in patients with thyroid nodules (TN) and Hashimoto’s Thyroiditis (HT) at the first clinical evaluation compared to TN patients without thyroid autoimmunity and HT patients without TN followed-up for 1-9 years.

Introduction. Several studies suggest a significant association between Hashimoto’s thyroiditis (HT) and thyroid cancer, but this relationship needs confirmation. In this study we compared the prevalence of thyroid cancer in HT associated to thyroid nodules vs HT without thyroid nodules at the first diagnosis and during the follow-up. Methods. A total of 484 patients with a diagnosis of HT at their first clinical evaluation were subdivided into two groups: 243 HT patients without thyroid nodules (HTN-) and 241 with one or more nodules (HTN+). FT3, FT4, TSH Tg/TPO-autoantibodies and thyroid ultrasound were performed in all cases; fine needle aspiration cytology (FNAC) were performed in 155 patients with TN and 74 patients underwent surgery. This last group was compared to a group of 161 patients with TN submitted to FNAC without any evidence of associated thyroid autoimmunity (NHTN+). Results. HTN+ patients had higher prevalence of suspicious/malignant cytology (Tir 4-5) (HTN+ 44/152 = 28.9%) compared to NHTN+ patients (12/161 = 7.4%, p<0.0001). In the group submitted to thyroidectomy, malignant histology was found in 48/74 (64.9%) HTN+ and in 16/37 (43.3%) NHTN+ patients (p<0.05). The histotype distribution was 44 papillary (PTC), 2 follicular (FTC), 2 medullary (MTC) thyroid carcinomas in HTN+ and 13 PTC, 2 FTC, 1 MTC in NHTN+ patients, PTC being the only tumor significantly associated to HT. Interestingly, the prevalence of multicentric PTC was significantly higher (14.4%) in HTN+ than in NHTN+ (5.6%) patients (p=0.0085). Finally, in the HTN- group, a minority (22/130 = 17%) of patients with available follow-up (1-9 years) developed one or more TN, but only 3 of them required FNAC which resulted benign (Tir-2) in all cases. None of these patients was submitted to thyroidectomy. Conclusion. This study confirms a higher prevalence of PTC in patients with HT associated to TN at the first clinical evaluation, compared to patients without thyroid autoimmunity. Conversely, no evidence of increased prevalence of thyroid malignancy was found in patients with HT without associated nodules at the first clinical evaluation during the first years of follow-up. This study might provide a clue to understand the association between HT and thyroid cancer.