Breast cancer in hypothyroid women using thyroid supplements

Area of Science:

• Endocrinology
• Oncology
• Epidemiology

Background:

• Iatrogenic hypothyroidism is often treated with thyroid supplementation.
• The potential association between thyroid hormone replacement therapy and breast cancer risk requires investigation.

Purpose of the Study:

• To investigate the risk of breast cancer in women receiving thyroid supplementation for iatrogenic hypothyroidism.

Main Methods:

• A cohort study was conducted at the Mayo Clinic, Rochester, Minn.
• Observed breast cancer cases in 1,665 hypothyroid women were compared to expected cases using standardized incidence ratios (SIR).
• Risk factors and management of hyperthyroidism/hypothyroidism were analyzed.

Main Results:

• The standardized incidence ratio (SIR) for breast cancer in hypothyroid women was 0.9 (47 observed vs. 52.9 expected).
• No increased breast cancer risk was observed in euthyroid women (SIR = 1.0).
• Breast cancer risk was not significantly influenced by hyperthyroidism management or hypothyroidism factors, except for a history of breast biopsy.

Conclusions:

• Thyroid supplementation for iatrogenic hypothyroidism does not appear to increase the risk of breast cancer.
• The findings suggest that thyroid hormone replacement therapy is safe concerning breast cancer development.