Levothyroxine use and the risk of breast cancer: a nation-wide population-based case–control study

Thyroid hormone enhances estrogen-mediated proliferation and cell cycle regulatory pathways in steroid receptor-positive breast Cancer

Estrogen receptor (ER) α expression and associated signaling is a major driver of over two-thirds of all breast cancers (BC). ER targeting strategies are typically used as a first-line therapy in patients with steroid receptor positive (SR+) disease. Secondary resistance to anti-estrogenic agents may occur with clonal expansion and disease progression. Mechanisms underlying hormone resistance are an expanding field of significant translational importance. Cross-talk with other nuclear hormones, receptors, and signaling pathways, including thyroid hormones (TH) and their receptors (THRs), have been shown to promote endocrine therapy resistance in some studies. We have shown that TH replacement therapy (THRT) was independently and significantly associated with higher rates of relapse and mortality in SR positive (+), node-negative (LN-) BC patients, whereas it showed no association with outcomes in SR negative (-) patients. LN-, SR+ patients receiving THRT and tamoxifen had the worst outcomes, suggesting a pro-carcinogenic interaction that significantly and independently shortened survival and increased mortality. Using in vivo and in vitro models, we previously showed hormonal cross-talk, altered gene signaling, target gene activation, and resistance to tamoxifen in the presence of TH. In this report, we show TH ± E2 ± tamoxifen inhibits cell cycle control signaling, reduces apoptosis, and enhances cell proliferation, tumor growth, tamoxifen resistance, and clonal expansion. Mechanistically these changes involve numerous genes and pathways, including critical cell cycle regulatory proteins and genes identified using various molecular methods. These studies facilitate a greater mechanistic understanding of the biological and molecular impact of TH on SR+ BC.

(Thyroid) Hormonal regulation of breast cancer cells

Thyroid hormone as L-thyroxine (T4) acts nongenomically at physiological concentrations at its cancer cell surface receptor on integrin αvβ3 ('thyrointegrin') to cause cancer cell proliferation. In the case of estrogen receptor (ERα)-positive breast cancer cells, T4 via the integrin promotes ERα-dependent cancer growth in the absence of estrogen. Thus, tumor growth in the post-menopausal patient with ERα-positive cancer may again be ER-dependent because of T4. Additional mechanisms by which T4 may contribute uniquely to aggressive breast cancer behavior-independently of ER-are stimulation of immune checkpoint inhibitor gene expression and of several anti-apoptosis mechanisms. These observations may call for consideration of elimination of host T4 production in breast cancer patients whose response is suboptimal to standard chemotherapy regimens. Euthyroidism in such a setting may be maintained with exogenous 3,3',5-triiodo-L-thyronine (T3).

Effects of thyroxine on apoptosis and proliferation of mammary tumors

Hypothyroidism is a protective factor against breast cancer but long-term exposure or overdoses of thyroid replacement therapy with thyroxine (T₄) may increase breast cancer risk.

OBJECTIVE

to study, in vivo and in vitro, the effects of T4 on the proliferation and apoptosis of mammary tumors of hypo- and euthyroid rats, and the possible mechanisms involved in these effects.

MATERIAL AND METHODS

Female Sprague-Dawley rats were treated with a single dose of dimethylbenzathracene (15 mg/rat) at 55 days of age and were divided into three groups: hypothyroidism (HypoT; 0.01% 6-N-propyl-2-thiouracil -PTU- in drinking water, n = 20), hypothyroidism treated with T₄ (HypoT + T₄; 0.01% PTU in drinking water and 0.25 mg/kg/day T₄ via sc; n = 20) and EUT (untreated control, n = 20). At sacrifice, tumor explants from HypoT and EUT rats were obtained and treated either with 10^-10 M T₄ in DMEM/F12 without phenol red with 1% Charcoalized Fetal Bovine Serum or DMEM/F12 only for 15 min to evaluate intracellular signaling pathways associated with T₄, and 24 h to evaluate changes in the expression of hormone receptors and proteins related to apoptosis and proliferation by immunohistochemistry and Western Blot.

RESULTS

In vivo, hypothyroidism retards mammary carcinogenesis but its treatment with T₄ reverted the protective effects. In vitro, the proliferative and anti-apoptosis mechanisms of T₄ were different regarding the thyroid status. In EUT tumors, the main signaling pathway involved was the cross-talk with other receptors, such as ERα, PgR, and HER2. In HypoT tumors, the non-genomic signaling pathway of T₄ was the chief mechanism involved since αvβ3 integrin, HER2, β-catenin and, downstream, PI3K/AKT and ERK signaling pathways were activated.

CONCLUSION

T₄ can regulate mammary carcinogenesis by mainly activating its non-genomic signaling pathway and by interacting with other hormone or growth factor pathways endorsing that overdoses of thyroid replacement therapy with T4 can increase the risk of breast cancer.

Thyroid Hormone Replacement Therapy Is Associated with Longer Overall Survival in Patients with Resectable Gastroesophageal Cancer: A Retrospective Single-Center Analysis

INTRODUCTION

As thyroid hormones modulate proliferative pathways it is surmised that they can be associated with cancer development. Since the potential association of gastroesophageal cancer and thyroid disorders has not been addressed so far, the aim of this study was to investigate the association of thyroid hormone parameters with the outcome of these patients, so novel prognostic and even potentially therapeutic markers can be defined.

MATERIAL AND METHODS

Clinical and endocrinological parameters of patients with resectable gastroesophageal cancer treated between 1990 and 2018 at the Vienna General Hospital, Austria, including history of endocrinological disorders and laboratory analyses of thyroid hormones at first cancer diagnosis were investigated and correlated with the overall survival (OS).

RESULTS

In a total of 865 patients, a tendency towards prolonged OS in hypothyroid patients (euthyroid, n = 647: median OS 29.7 months; hyperthyroid, n = 50: 23.1 months; hypothyroid, n = 70: 47.9 months; p = 0.069) as well as a significant positive correlation of thyroid hormone replacement therapy with the OS was observed (without, n = 53: median OS 30.6 months; with, n = 67: 51.3 months; p = 0.017). Furthermore, triiodothyronine (T3) levels were also associated with the OS (median OS within the limit of normal: 23.4, above: 32.4, below: 9.6 months; p = 0.045).

CONCLUSIONS

Thyroid disorders and their therapeutic interventions might be associated with the OS in patients with resectable gastroesophageal cancer. As data on the correlation of these parameters is scarce, this study proposes an important impulse for further analyses concerning the association of thyroid hormones with the outcome in patients with gastroesophageal tumors.

Risk of Breast Cancer in Females With Hypothyroidism: A Nationwide, Population-Based, Cohort Study

OBJECTIVES

The results of studies investigating the relationship between breast cancer and hypothyroidism vary greatly from study to study. In this study, we analyzed a large and reliable, population-based database to gain a better understanding of the correlation.

METHODS

This retrospective cohort study analyzed patients with hypothyroidism between January 1, 2000 and December 31, 2012 (hypothyroidism cohort) from the Longitudinal Health Insurance Database 2000 in Taiwan. For each woman with hypothyroidism, 1 woman without a history of breast cancer was randomly selected from the Longitudinal Health Insurance Database 2000 and frequency matched (1:4) with women without hypothyroidism by age and index year of hypothyroidism. The study outcome was the diagnosis of breast cancer during a 12-year follow-up period.

RESULTS

In this study, 6665 women with hypothyroidism and 26 660 women without hypothyroidism were identified. The hypothyroidism cohort had a significantly higher risk of breast cancer than the nonhypothyroidism cohort (adjusted hazard ratio [aHR] 1.69 [95% CI, 1.15-2.49]; P = .01), especially in the group aged 40 to 64 years (aHR 2.07 [95% CI, 1.32-3.23]; P = .01). Women in the hypothyroidism cohort taking levothyroxine for a duration ˃588 days showed a significantly decreased risk of breast cancer (aHR 0.37 [95% CI, 0.19-0.71]; P = .003).

CONCLUSION

Women with hypothyroidism are at a higher risk of breast cancer than those without hypothyroidism. Levothyroxine may reduce the risk of breast cancer in a woman with hypothyroidism.

Levothyroxine treatment is associated with an increased relative risk of overall and organ specific incident cancers - a cohort study of the Swedish population

High thyroid hormone values have been associated with an increased risk of incident cancers, especially breast cancer but also lung cancer and any solid cancers. We explored whether there is an increased risk of overall and cause-specific cancers in those receiving levothyroxine treatment. We included all individuals ≥ 18 years in Sweden (N = 8,573,313) on January 1 2009, and identified patients with two or more dispensed prescriptions of levothyroxine 2005-2006 (n = 253,193, 3.0 %). A cancer diagnosis in the Swedish Cancer Register 2009-2015 was used as outcome. We excluded patients with a cancer diagnosis before 2005. Cox regression was used (hazard ratios, HRs, and 95 % confidence intervals, CI) with adjustments for age, socioeconomic/neighborhood factors and co-morbidities. Totally 399,751 cases of incident cancer were identified, with a slight increased overall risk associated with levothyroxine treatment for both men, adjusted HR 1.06 (95 % CI 1.03-1.10), and women, adjusted HR 1.08 (95 % CI 1.07-1.10). For men, increased risks were found for cancers of the thyroid gland and other endocrine glands. For women, increased risks were found for cancers of the breast, endometrium, other female genitals (ovaries not included), stomach, colon, liver, pancreas, urinary bladder, skin, leukemia, and unspecified primary tumor. Unlike men, for women, no increased risk was found for cancer of the thyroid gland. In conclusions, levothyroxine treatment was associated with an excess cancer risk, including many different types of cancer, especially among women. Our results need confirmation by other studies, but levothyroxine is recommended to be prescribed only on approved indications.

What Can We Learn About Drug Safety and Other Effects in the Era of Electronic Health Records and Big Data That We Would Not Be Able to Learn From Classic Epidemiology?

As more and more health systems have converted to the use of electronic health records, the amount of searchable and analyzable data is exploding. This includes not just provider or laboratory created data but also data collected by instruments, personal devices, and patients themselves, among others. This has led to more attention being paid to the analysis of these data to answer previously unaddressed questions. This is especially important given the number of therapies previously found to be beneficial in clinical trials that are currently being re-scrutinized. Because there are orders of magnitude more information contained in these data sets, a fundamentally different approach needs to be taken to their processing and analysis and the generation of knowledge. Health care and medicine are drivers of this phenomenon and will ultimately be the main beneficiaries. Concurrently, many different types of questions can now be asked using these data sets. Research groups have become increasingly active in mining large data sets, including nationwide health care databases, to learn about associations of medication use and various unrelated diseases such as cancer. Given the recent increase in research activity in this area, its promise to radically change clinical research, and the relative lack of widespread knowledge about its potential and advances, we surveyed the available literature to understand the strengths and limitations of these new tools. We also outline new databases and techniques that are available to researchers worldwide, with special focus on work pertaining to the broad and rapid monitoring of drug safety and secondary effects.