Supplementary Material for: TPOAb and Thyroid Function Are Not Associated with Breast Cancer Outcome: Evidence from a Large-Scale Study Using Data from the Taxotere as Adjuvant Chemotherapy Trial (TACT, CRUK01/001)

<b><i>Background:</i></b> Small-scale studies correlated the presence of thyroid autoimmunity with both improved or worsened breast cancer outcome. <b><i>Objectives:</i></b> We aimed to clarify this association in a large cohort using the phase III, randomized, controlled Taxotere as Adjuvant Chemotherapy Trial (TACT, CRUK01/001). <b><i>Methods:</i></b> TACT women &gt;18 years old with node-positive or high-risk node-negative early breast cancer (pT1–3a, pN0–1, M0), with stored plasma (<i>n</i> = 1,974), taken 15.5 (median; IQR 7.0–24.0) months after breast surgery were studied. Patients had also received chemotherapy (100%), radiotherapy (1,745/1,974; 88.4%), hormonal therapy (1,378/ 1,974; 69.8%), or trastuzumab (48/1,974; 2.4%). History of thyroid diseases and/or related treatments was not available. The prognostic significance of autoantibodies to thyroid peroxidase (TPOAb; positive ≥6 kIU/L), free-thyroxine and thyrotropin (combined: euthyroid, hypothyroid, hyperthyroid) was evaluated for disease-free survival (DFS), overall-survival (OS), and time-to-recurrence (TTR), with Cox regression models in univariate and multivariable analyses. The extended median follow-up was 97.5 months. <b><i>Results:</i></b> No difference in DFS was found by TPOAb status (unadjusted hazard ratio [HR]: 0.97, 95%CI: 0.78–1.19; <i>p</i> = 0.75) and/or thyroid function (unadjusted HR [hypothyroid vs. euthyroid]: 1.15, 95% CI: 0.79–1.68; <i>p</i> = 0.46; unadjusted HR [hyperthyroid vs. euthyroid]: 1.14, 95% CI: 0.82–1.61; <i>p</i> = 0.44). Similar results were obtained for OS, TTR, multivariable analyses, when TPOAb titre by tertiles was considered, and in a subgroup of 123 patients with plasma collected before adjuvant treatments. <b><i>Conclusions:</i></b> No evidence for a prognostic role of TPOAb and/or thyroid function in moderate-to-high-risk early breast cancer was found in the largest and longest observational study to date.