Clinical Significance of Diffuse Thyroid Uptake on FDG PET/CT in Triple Negative Breast Cancer Patients

Objectives Therapy-induced thyroid autoimmunity was allegedly related with favorable outcomes in several malignancies. Clinical significance of diffuse thyroid uptake (DTU) on FDG PET/CT that is indicative of thyroid autoimmunity was investigated in patients with breast cancer.

Methods Among 103 patients who underwent FDG PET/CT for breast cancer at our institute from 2006 to 2014, 99 patients who completed planned treatment including surgery, chemotherapy, and radiation were retrospectively enrolled for the study. Thyroid uptake was evaluated on FDG PET/CT, thyroid USG, and thyroid function tests (TFT) including anti-thyroid peroxidase (TPO) antibodies, anti-thyroid antibodies (TAb) were analyzed. Subgroup analysis was performed according to the molecular subtype based on hormonal status; estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2).

Results Among 99 patients (47.0 ± 8.9 y), TNM staging was stage I 18 %, stage II 43 %, and stage III 39 %, respectively. Molecular subtypes were luminal type 49 %, HER2 type 24%, triple negative (TN) 23%, respectively. FDG PET/CT (1.8 ± 1.2 times) performed for the evaluation of therapy response (44.4 ± 33.6 m), and DTU appeared in 44 patients. Two cancer-related deaths were reported, and disease progression was identified in 34 patients during the follow-up (87.6 ± 37.2 m). No significant parameters including DTU, hormonal status, and TFT was related with progression-free survival (PFS) in the whole patients. However, in a subgroup of TN breast cancer (TNBC) patients, PFS (TNBC vs non-TNBC, 7.3 ± 3.2 vs 7.0 ± 3.1, p = 0.812) was significantly associated with DTU (p < 0.009) and anti-TPO antibodies (p < 0.022), respectively. In this subgroup, Tab also showed a considerable trend toward significance (p = 0.088). Multivariate analysis revealed that only DTU was significant factor for PFS (OR = 0.192, p < 0.019). Chi-square test proved that both anti-TPO antibodies (kappa = 0.488, p = 0.000) and Tab (kappa = 0.427, p = 0.000) showed moderate agreements with DTU.

Conclusions Appearance of DTU on FDG PET/CT for the evaluation of therapy response that showed agreements with thyroid-related autoantibodies was significantly related with PFS of TNBC patients. Therapy-induced thyroid autoimmunity might mediate favorable outcome in TNBC patients.