INVESTIGATING THE ASSOCIATION BETWEEN HYPOTHYROIDISM AND BREAST CANCER PROGNOSIS IN WOMEN UNDERGOING ENDOCRINE THERAPY: A NARRATIVE REVIEW

Background: Hypothyroidism is a prevalent endocrine disorder that may affect treatment outcomes in breast cancer patients, particularly those receiving endocrine therapy. As both conditions commonly coexist in women and share hormonal pathways, understanding their interaction is increasingly relevant to clinical decision-making and survivorship care. Objective: This narrative review aims to explore the influence of hypothyroidism on prognosis, recurrence, and therapeutic outcomes in women undergoing endocrine therapy for breast cancer. Main Discussion Points: The review synthesizes recent evidence across several key themes: the impact of radiation-induced hypothyroidism, the biological role of thyroid hormones in breast cancer progression, and the potential influence of thyroid hormone replacement—particularly levothyroxine—on endocrine therapy efficacy. It also addresses the limitations of current studies, including methodological inconsistencies, limited prospective data, and poor generalizability. Mechanistic insights suggest a complex interaction between thyroid and estrogen receptor signaling, which may influence tumor behavior and treatment response. Conclusion: While evidence supports routine thyroid monitoring and consideration of thyroid-sparing techniques in radiotherapy, conclusive data on the prognostic significance of hypothyroidism remain limited. Future prospective trials and mechanistic studies are essential to inform clinical guidelines and optimize personalized care.