LAKE BUENA VISTA, FLA. – In contrast with at least two prior small studies, thyroid peroxidase autoantibodies were not associated with breast cancer outcomes in a large cohort of patients.
Stored serum samples from 1,974 patients with lymph node–positive or high-risk lymph node–negative breast cancer who were enrolled in the TACT (Taxotere as Adjuvant Chemotherapy for Early Breast Cancer) trial were tested, and investigators assessed the prognostic significance of thyroid peroxidase autoantibodies (TPOAb) and thyroid function for disease-free survival (DFS), overall survival (OS), and time to recurrence (TTR).
Dr. Ilaria Muller
At a median follow-up of 97.5 months, investigators found no evidence of a difference in outcomes, either on univariate or multivariable analysis, for any of those outcomes based on free thyroxine (FT4) or thyroid-stimulating hormone (TSH) levels alone or in combination as hypo- or hyperthyroidism, Dr. Ilaria Muller, of Cardiff (England) University reported at the International Thyroid Congress.
For example, the unadjusted hazard ratios for DFS, OS, and TTR based on TPOAb-positive vs. TPOAb-negative status were 0.97, 0.86, and 0.97, respectively, Dr. Muller said.
An explorative multivariable analysis of the impact of TPOab status and thyroid function on breast cancer DFS, OS, and TTR also showed no evidence of a difference (HR, 1 and 0.97 for TPOAb-negative and TPOAb-positive status; HR, 1 and 1.27 for euthyroid and hypothyroid status), Dr. Muller said.
Similarly, no evidence of a difference in outcomes was seen based on an explorative analysis of TPOAb status in clinical subgroups based on age, nodal status, tumor grade, tumor size, type of surgery, estrogen receptor (ER)-positive status, human epidermal growth factor receptor 2 (HER2)-positive status, and molecular subgroup, she noted.
Serum samples used in the study were from patients who had undergone breast cancer surgery a mean of 15.5 months prior and were mainly taken during/after adjuvant treatments for breast cancer. All had received chemotherapy: 88.4% received radiotherapy, 98.7% of ER-positive patients received hormonal therapy, and trastuzumab was given in 11.8% of HER2-positive patients.
About a fifth (20.6%) of patients were TPOAb-positive, 89.16% were euthyroid, 4.86% were hypothyroid, and 5.97% were hyperthyroid.
The TPOAb-positive and -negative patients were largely comparable, except the TPOAb-positive women were slightly older.
A sensitivity analysis performed in 123 patients with blood taken after surgery but before any adjuvant therapy for breast cancer also showed no evidence of TPOAb prognostic ability, Dr. Muller said.
Despite an ongoing debate aabout a possible association between breast cancer and thyroid autoimmunity, findings have been conflicting. Two small studies correlated TPOAb positivity with improved breast cancer outcomes, but a third did not confirm the findings.
“As a possible explanation, we hypothesized an immune response to shared thyroid/breast antigens. We recently reported that TPO is expressed in breast cancer tissue,” Dr. Muller wrote.
However, the findings of the current study – the largest retrospective study to date investigating the prognostic role of TPOAb in breast cancer – suggest that TPOAb and thyroid function are not prognostic markers in breast cancer.
“Effects of chemotherapy and/or radiotherapy for breast cancer are currently under debate. Tamoxifen exerts an antithyroid effect. However, confounding due to breast cancer adjuvant treatment is unlikely to alter significantly any results, as suggested by our sensitivity analysis performed on 123 patients,” she said at the meeting held by the American Thyroid Association, Asia-Oceania Thyroid Association , European Thyroid Association, and Latin American Thyroid Society.
This study was supported by a Tenovus Innovation Grant from Tenovus Cancer Care. TACT was funded by Cancer Research UK. Dr. Muller reported having no disclosures.