Higher-but-within-normal TSH is associated with higher risk for differentiated thyroid cancer (DTC) in surgical series. Our recent clinical observations suggest that this is not the case in the presence of autoimmune thyroid disease (AITD). We designed the present study to clarify this controversy.
We analyzed our prospectively collected database of patients referred for thyroid surgery at two tertiary care referral centers in Greece and the USA. We collected data for, preoperative TSH, postoperative pathology and Thyroid Peroxidase (TPO) antibodies titers. Subjects were subdivided into two groups, those with autoimmune thyroid disease (AITD, i.e. lymphocytic thyroiditis) and Non-AITD. We excluded subjects with Graves disease, abnormal TSH (<0.40 or >4.50mIU/mL) or recent use of levothyroxine. We compared the serum TSH among different groups using the Mann Whitney test.
3973 subjects were studied. 1357 were excluded. Data from 1731 Non-AITD subjects and 329 AITD subjects were included in the analysis. AITD subjects had higher TSH than Non-AITD subjects (2.09 vs. 1.48 p<0.0001). TSH values were higher in DTC compared to benign histology only in non-AITD subjects (1.65 vs 1.40, p<0.0001). Progressively higher TSH was associated with higher incidence of DTC only in non-AITD subjects (p<0.0001). In AITD subjects, TSH was similar between groups with/without DTC (2.02 vs. 2.14, p=0.21).
TSH concentrations are not associated with the risk of developing DTC in the presence of thyroid autoimmunity, even though this seems to be the case for all other patients.

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