Risk of Adverse Cardiovascular Outcomes in Differentiated Thyroid Cancer Survivors: A Systematic Review and Meta-Analysis

Association Between Serum Thyrotropin and Cancer Recurrence in Differentiated Thyroid Cancer: A Population-Based Retrospective Cohort Study

Background: Levothyroxine to suppress thyrotropin (TSH) to <0.5 mIU/L following thyroidectomy in differentiated thyroid cancer (DTC) may reduce recurrence in higher-risk DTC. However, there is limited evidence to support guideline recommendations to maintain TSH in the low-normal range of 0.5-2 mIU/L to reduce recurrence in patients with lower risk DTC. The primary objective was to assess the association between exposure to high normal serum TSH (2-4 mIU/L) as compared with low normal TSH (0.5-2 mIU/L) target ranges and cancer recurrence in patients with DTC after thyroidectomy. Methods: This population-based retrospective cohort study used linked, administrative health care databases from Ontario, Canada, to follow patients with DTC post-thyroidectomy from 2007 to 2018. The exposure was time updated, serum TSH, treated as a cumulative and instantaneous exposure. Multivariable cause-specific proportional hazard regression analyses were performed to determine time to DTC recurrence from index date, defined as a composite of repeat neck surgery, radioactive iodine (RAI) treatment, and/or DTC-specific death. Results were also stratified by initial treatment as a marker of baseline recurrence risk in a sensitivity analysis. Results: This cohort of 26,336 individuals (78% female) with DTC and a median age of 50 years were followed for a median of 5.9 (interquartile range 3.6-8.6) years; 40.9% were initially treated with a hemi-thyroidectomy only and 38.2% received a total thyroidectomy and RAI. Compared with exposure to TSH 0.5 to ≤2 mIU/L, DTC recurrence rate was similar for each additional 3 months of exposure to TSH >2 to ≤4 mIU/L (adjusted cause specific [cs] hazard ratio [HR] 0.99 [confidence interval or CI 0.97-1.02]) but was significantly increased with each additional 3 months of exposure to TSH >4 mIU/L (adjusted csHR 1.07 [CI 1.04-1.09]). Results were similar across baseline treatment groups. Conclusion: There was no difference in clinically significant recurrence in those with low-risk DTC maintained with a TSH of 0.5-2 mIU/L compared with 2-4 mIU/L. Guidelines should consider liberalizing target TSH level post thyroidectomy in low-risk cohorts. These results cannot be applied to patients with high-risk DTC.

The Effect of Thyrotropin Suppression on Survival Outcomes in Patients with Differentiated Thyroid Cancer: A Systematic Review and Meta-Analysis

Background: Long-term management of intermediate- and high-risk differentiated thyroid cancer (DTC) involves thyrotropin (TSH) suppression with thyroid hormone to prevent potential stimulation of TSH receptors on DTC cells, leading to tumor growth. However, the current guidelines recommending TSH suppression are based on low- to moderate-quality evidence. Methods: We performed a systematic review and meta-analysis of studies evaluating the role of TSH suppression in intermediate- and high-risk DTC patients (≥18 years) treated as per regional guideline-based therapy with a follow-up duration of 5 years (PROSPERO #252396). TSH suppression was defined as "below normal reference range" or, when known, <0.5 mIU/L. Primary outcome measures included (i) composite of progression-free survival (PFS), disease-free survival (DFS), and relapse-free survival (RLFS), and (ii) composite of disease-specific survival (DSS), and overall survival (OS). Secondary outcome included a composite of cardiac or skeletal adverse events. All outcomes and comparisons were represented as TSH suppression versus TSH nonsuppression. Randomized controlled trials, cohort studies, and case-control studies were included for analysis. Pooled hazard ratio (HR) and 95% confidence interval (CI) were calculated using random-effects model. Results: Abstract screening was performed on 6,369 studies. After the exclusion of irrelevant studies and full-text screening, nine studies were selected for the final meta-analysis. Based on seven studies (3,591 patients), the composite outcome of PFS, DFS, and RLFS was not significantly different between TSH suppression and nonsuppression groups (HR: 0.75; 95% CI: 0.48-1.17; I2 = 76%). Similarly, a DSS and OS composite outcome assessment based on four studies (3,616 patients) did not favor TSH suppression (HR: 0.69; 95% CI: 0.31-1.52; I2 = 88%). Even after excluding studies of lower quality, the primary outcomes were not significantly different between the TSH suppression and nonsuppression cohorts. The secondary outcome, obtained from two studies (1,294 patients), was significantly higher in the TSH-suppressed groups (HR: 1.82; 95% CI: 1.30-2.55; I2 = 0%). Significant study heterogeneity was noted for primary outcomes. Conclusion: TSH suppression in intermediate- and high-risk DTC may not improve survival outcomes but may increase the risk of secondary complications. However, the limited evidence and study heterogeneity warrant cautious interpretation of our findings. Registration: PROSPERO #252396.

Thyroid cancer and cardiovascular diseases: a Mendelian randomization study

Background

Multiple observational studies have shown associations between thyroid cancer (TC) and cardiovascular diseases (CVDs). However, the results were inconsistent, and the potential causal genetic relationship remains unclear.

Methods

The genetic instruments of TC and CVDs were derived from data obtained through genome-wide association studies (GWAS). We performed the two-sample Mendelian randomization(MR) methods to investigate the causality of TC on CVDs. Summary-level statistics for CVDs, including heart failure (HF), atrial fibrillation (AF), coronary artery disease (CAD), myocardial infarction (MI), ischemic stroke (IS) and venous thromboembolism (VTE). The primary method employed in this MR analysis was the Inverse Variance Weighted (IVW) approach, and four additional algorithms were used: MR-Egger, weighted median, simple mode, and weighted mode. Additionally, we assessed the reliability of the causal relationship through pleiotropy, heterogeneity and leave-one-out sensitivity analysis.

Results

In this MR analysis, we only detected causality of genetically predicted TC on HF (IVW method, odds ratio (OR) = 1.00134, 95% confidence interval (CI): 1.00023-1.00244, p = 0.017). However, There were no causal associations of TC with CAD, MI, AF, IS, and VTE.

Conclusion

Our results confirmed the causal association between TC and HF. It is crucial to closely monitor the incidence of HF in TC patients and give comprehensive clinical intervention based on conventional treatment.

Preliminary Results of a Double-Blind Randomized Controlled Trial Evaluating the Cardiometabolic Effects of Levothyroxine and Liothyronine Compared to Levothyroxine with Placebo in Athyreotic Low-Risk Thyroid Cancer Patients

Background: Evidence is needed on the risks and benefits of combination therapy with levothyroxine (LT4)+liothyronine (LT3) for the treatment of hypothyroidism. Objective and Methods: We performed a randomized, double-blind placebo-controlled study to assess the effects of LT4+LT3 therapy versus LT4+placebo in a homogeneous group of athyreotic patients, without cardiovascular risk factors during long-term replacement monotherapy with LT4. The primary objective of the study was to assess the effects of combination LT4+LT3 therapy on heart rate, cardiac rhythm, and sensitive cardiovascular parameters of cardiac morphology and function by means of electrocardiography and Doppler echocardiography. The secondary objective of the study was to evaluate patient compliance, tolerability, and potential adverse events. Results: Thirty-eight patients with postsurgical hypothyroidism satisfying the inclusion criteria were selected from a group of 300 patients with low-risk thyroid cancer followed for a routine follow-up; they were randomized to receive LT4+LT3 or LT4+placebo. Twenty-four patients were evaluated after 1 year of treatment. All clinical and laboratory parameters were compared with the results obtained from 50 healthy euthyroid volunteers without comorbidities, matched for gender, age, physical activity, and lifestyle. Participants and clinicians remained blinded to the treatment allocation. After 1 year of combination therapy, a significant improvement in the diastolic function, evidenced by a significant reduction in the E/e' ratio (p = 0.046) and its positive trend over time, was observed in the LT4+LT3 group versus the LT4+placebo group. In addition, the univariate analyses showed a significant relationship between free triiodothyronine (fT3) levels (in pg/mL) with Δ of variation of the E/e' ratio in the LT4+LT3 group (standardized β coefficient = 0.603 [confidence interval: 0.001-1.248], p = 0.050) after combination therapy. No adverse events including tachycardia, arrhythmias, atrial fibrillation, or other important events occurred between the first administration and the end of the study. Conclusions: In this preliminary report, combination treatment with LT4+LT3 induced favorable changes in cardiovascular parameters of diastolic function without any adverse cardiovascular events. Trial Registration: EUDRACT number: 2017-001261-25.