Study of Euthyroid Hypothyroxinemia in Metastatic Breast Carcinoma (B-TREUH)

Up to one third of breast cancer patients have hypothyroidism or hyperthyroidism. L-thyroxine (T4), or Synthroid, is the most commonly prescribed agent for the management of hypothyroidism in the US. However, there are data suggesting that triiodothyronine (T3) may have benefits in preventing disease progression over l-thyroxine (T4).

It is estimated that there are approximately 155,000 living with metastatic breast cancer in the US and the number is estimated to increase over the next years (SEER data). Although their median survival has improved over the last 2 decades from 17 months to approximately 24 months attributed to newer treatments, there is an ongoing need for additional strategies and research to improve survival and quality of life. Many studies have explored the connection between hypothyroidism and hyperthyroidism and breast cancer with varied results ranging up to one third prevalence. Low Triiodothyronine (T3) and elevated Thyroid-Stimulating Hormone (TSH) levels have been detected in newly diagnosed breast cancer patients. Other studies have suggested that some of the common symptoms reported by breast cancer survivors such as fatigue and depression can be attributed to subclinical hypothyroidism. L-thyroxine (T4) is the most commonly prescribed agent for the management of hypothyroidism in the US. However, there are data suggesting that T4 is a potent pro-oncogenic agent. Proposed mechanisms include stimulation of mitogenesis, angiogenesis and resistance to apoptosis, opposition of anti-PDL-1 and radiation effects. It has been postulated that the avbeta3integrin that is universally expressed on cancer cells harbors a thyroid hormone receptor and T4 interacts with it. Triiodothyronine (T3) on the other hand, is significantly less oncogenic and less mitogenic and is downstream of T4 which is a T3 pro-hormone. Therefore, exogenous supplementation of T3 would decrease the T4 levels creating the desired state of euthyroid hypothyroxinemia. The rationale of this study is to replace L-thyroxine (T4) with Triiodothyronine (T3) in hypothyroid patients with metastatic breast carcinoma while they continue to receive standard systemic therapy, titrating the dose to achieve a state of euthyroid hypothyroxinemia which is turn would result in a lower risk of disease progression and improved survival by lowering the concentration of T4.

Following discontinuation of L-thyroxine (T4), triiodothyronine (T3) will be initiated at a 3:1 ratio. The dose will be titrated by the investigator to maintain levels of free T4 < 50% of normal range while maintaining a euthyroid state. Triiodothyronine (T3) tablets for oral administration will be prescribed once or twice daily depending on the total dose. Treatment duration will be approximately 9 months during which time the subjects will continue to be treated and monitored as usual for their metastatic breast cancer. During the study period and at the conclusion of the study period, there will be continuous evaluations of the disease status and thyroid status with the option of resuming the original thyroid replacement or continuation of the triiodothyronine (T3).

Participants will have their L-thyroxine (T4) discontinued and Triiodothyronine (T3)/liothyronine sodium initiated at 3: 1 and titrated.

Number of Participants With Progression-free Survival at 12 Months Based Upon Clinical and Radiological Assessments Completed as Part of Routine Care

To prospectively evaluate the progression-free survival in hypothyroid patients with metastatic breast carcinoma who are rendered euthyroid and hypothyroxinemic. Progression is defined using Response Evaluation Criteria in Solid Tumors Criteria (RECIST v1.1), as a 20% increase in the nadir sum of the longest diameter (SLD) of target lesions, or unequivocal progression (overall level of substantial worsening) in existing non-target lesions, or the appearance of one or more new lesions.

To quantitate the prevalence of hypothyroidism in metastatic breast cancer patients at a community oncology practice.

Study duration, planned was 48 months but actual was 36 months [March 1, 2019 to March 9, 2022] due to premature closure due to planned relocation of the PI.

Functional Assessment of Cancer Therapy - Breast (FACT-B) Total Score comprised of Physical Well Being (PWB), Social Well Being (SWB), Emotional Well Being (EWB), Functional Well Being (FWB), and Breast Cancer Subscale (BCS). Range is 0-148. A higher score indicates higher quality of life. Missing scores were handled by prorating values.

Functional Assessment of Cancer Therapy - Breast (FACT-B) Lack of energy on 5 point Likert scale as measured on FACT-B Physical Well-being subscale. Score of 0 indicates no lack of energy with score of 4 indicating total lack of energy.

To study the average time required to achieve euthyroid hypothyroxinemia state in qualifying patients. Thyroid function laboratory testing was performed at baseline and then at every 4 weekly intervals until 12 weeks then every 3 monthly thereafter, unless thyroid-stimulating hormone (TSH) was abnormal. If a normal TSH level was not achieved by the 12 week visit, repeat TSH measurements were ordered every 4-6 weeks until the TSH value was within the laboratory normal reference range. Initial euthyroid state defined by number of days between initiation of triiodothyronine (T3) and documentation of first normal TSH value.

Number of days between initiation of triiodothyronine (T3) and documentation of first normal TSH value for each participant, assessed up to 12 months

Inclusion Criteria: Age greater than or equal to 18 Male or female with diagnosis of metastatic breast carcinoma and documented history of hypothyroidism . TSH level within normal range at baseline Life expectancy estimated > 3 months Ability and willingness to provide informed consent Exclusion Criteria: Life expectancy estimated to be less than 3 months Is currently pregnant or intends to become pregnant during the duration of the study Active angina, New York Heart Association (NYHA) advanced [Class III/IV] congestive heart failure, or uncontrolled cardiac arrhythmia within 6 months of enrollment History of thyrotoxicosis History of adrenal insufficiency Hypersensitivity to any active or extraneous constituents in Triiodothyronine (T3)/liothyronine sodium