Thyrotropin (TSH) and thyroid autoimmunity are predictive factors for the incidental discovery of papillary thyroid microcarcinoma during thyroidectomy.

Purpose: To identify clinical, biological and pathological risk factors for the incidental discovery of papillary thyroid microcarcinomas (PTMCs) in patients undergoing thyroidectomy for presumed benign conditions.

Methods: Cross sectional, single center study, involving all consecutive patients (N = 3015) who were submitted to thyroid surgery between 2001-2019. All medical files were retrospectively reviewed. A total of 1961 patients in the benign group and 145 patients in PTMC group were analyzed.

Results: No significant differences in age, sex, body mass index, smoking status, thyroid volume or weight and preoperative thyroxine treatment between benign and PTMC groups were observed. Circulating anti- thyroid antibodies, histological thyroiditis and serum thyrotropin (TSH) were significantly associated with PTMC in univariable analysis. Independent risk factors for incidental PTMC by multivariable analysis where possible (OR: 1.51, 95% CI: 0.99-2.28) and certain (OR: 1.74, 95% CI: 1.09-2.78) thyroid autoimmunity (p = 0.002) and higher serum TSH (OR: 1.25, 95% CI: 1.08-1.45, p = 0.03), whereas thyroid lobectomy was associated with a lower risk of PTMC (OR: 0.40, 95% CI: 0.24-0.67, p < 0.001). The most frequent genetic alteration was BRAF mutation, found in 56.3% of PTMC submitted to DNA sequencing. No association between clinical, biological or histological characteristics of PTMC and BRAF mutation was observed.

Conclusions: Thyroid autoimmunity and higher preoperative serum TSH level were independent predictors of PTMC incidentally discovered during thyroid surgery. Larger prospective studies are needed to better identify possible risk factors for papillary thyroid carcinoma initiation and progression.