Papillary thyroid cancer, although strongly associated with lymphocytic infiltration on histology, is only weakly predicted by serum thyroid auto-antibodies in patients with nodular thyroid diseases.

OBJECTIVE: We evaluated the association between thyroid autoimmunity and thyroid cancer in a retrospective series of unselected thyroid nodules submitted to fine-needle aspiration (FNA) cytology.
DESIGN: Anti-thyroid antibodies (TAb) were measured in patients with multinodular goiter (MNG) and single/isolated thyroid nodule (S/I) submitted to FNA. Thyroid lymphocytic infiltration (LI) on histology was studied in a subgroup of patients submitted to thyroidectomy; 13,021 patients were included: on cytology 622 had papillary thyroid cancer (c- PTC) and 12,399 benign thyroid nodular diseases (c-BTN). LI was evaluated in histological samples of 688 patients: 304 with PTC (h-PTC) and 384 with BTN (h-BTN).
RESULTS: TAb prevalence was not different in c-BTN and c-PTC (38.7% vs 35.6%). TAb were more frequent in c-BTN than c-PTC in females with MNG (40.1% vs 32.5%, p=0.02), and in c-PTC than in c-BTN in males with S/I (31.2% vs 20.4%, p=0.02) and, although not significantly, in females younger than 30 yr (35.1% vs 30.7%). The frequency and severity of LI was significantly higher in h-PTC than h-BTN, both in MNG (82.5% vs 45.0%, p<0.001) and S/I (85.6% vs 71.0%, p<0.001), but a higher number of patients with h-PTC had negative circulating TAb, despite the presence of moderate/severe LI.
CONCLUSIONS: TAb are weakly associated to PTC in males and young females, while they are more frequent in older females with BTN. The frequency and severity of LI is significantly higher in PTC than in BTN, but in cancer patients TAb are frequently negative, despite the evidence of histological thyroiditis. These data suggest that different kinds of immune response may be involved in PTC and BTN.