High prevalence of suspicious cytology in thyroid nodules associated with positive thyroid autoantibodies

Objective: The association between thyroid autoimmunity and thyroid cancer has been often suggested, but is difficult to prove due to selection bias of surgical series. Aim of this study was then to re-assess this association in a retrospective series of unselected thyroid nodules submitted to fine needle aspiration cytology (FNAC). Subjects and methods: We reviewed 590 ultrasound (US) guided FNACs obtained from unselected consecutive single thyroid nodules referred to our outpatient service from January 2002 to July 2004. Cytological results were classified in three classes of increased risk of malignancy: low risk or benign (class II); mild increased risk (class III) and suspect or malignant (class IV) nodules. Cytological results were analyzed according to the presence (ATA+ n=197) or absence (ATA- n=393) of associated serum anti-thyroid antibodies (ATA) as marker of thyroid autoimmunity. Results: The distribution of cytological classes within the study groups was as follows: Group ATA-: class II n=273 (69.5%), class III n=84 (21.4%) and class IV n=36 (9.2%); Group ATA+: class II n=103 (52.3%), class III n=57 (28.9%) and class IV n=37 (18.8%), corresponding to a significantly higher prevalence of class III (p<0.05) and class IV (p<0.001) in ATA+ nodules. The prevalence of class II nodules was significantly lower (p<0.001) in ATA+ patients. In 106 patients submitted to thyroidectomy, thyroid cancer was found in 54/61 (88.5%) patients with class IV cytology (without significant difference between ATA+ [96.4%] and ATA– [81.8%] nodules), and in 6/31 (19.3%) of class III nodules, exclusively in ATA-. Taken together, higher cancer prevalence, mostly represented by papillary thyroid carcinoma, was documented in ATA+ (27/197=13.7%), when compared to ATA– nodules (33/393=8.4%, p<0.05). Conclusions: The present study, performed on unselected consecutive thyroid FNACs, devoid of selection biases, showed increased frequency of suspect or clearly malignant FNACs in ATA+ nodules when compared to ATA-. According to histological results, this finding was not due to false positive FNACs and is in keeping with previous studies supporting a significant association between papillary thyroid carcinoma and thyroid autoimmunity.