Endocrine Abstracts

JOINT199

Background: The discovery of immune checkpoint inhibitors (ICIs), such as anti-PD-1/PD-L1 and anti-CTLA-4 antibodies, has vastly improved survival outcomes among patients diagnosed with triple-negative breast cancer. However, immunotherapy is associated with immune-related adverse effects (irAEs), among which thyroid dysfunction is one of the most common. Understanding the clinical presentation and management of immunotherapy-associated thyroid dysfunction is of utmost importance.

Case Presentation: We report the case of a 50-year-old female with triple-negative breast cancer who developed thyroid dysfunction following treatment with pembrolizumab, an anti-PD-1 inhibitor. Paradoxically, the patient was asymptomatic, except for persistent fatigue which she believed was a frequent side effect of the treatment. Laboratory results revealed an elevated TSH of 195 μIU/ml and suppressed free T4 of 1.30 pmol/l, consistent with severe hypothyroidism, while thyroperoxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb) were negative. Thyroid ultrasonography showed diffuse heterogeneity and almost no vascular flow. She was started on levothyroxine therapy with gradual dose escalation. The oncologist decided to continue immunotherapy despite thyroid dysfunction and suggested close monitoring of thyroid function and symptom management.

Discussion: This case highlights the importance of thyroid function evaluation during immunotherapy treatment, even in the absence of clinical manifestations. A multidisciplinary approach is needed in order to optimize patient care and outcomes.

Conclusion: Immunotherapy-related thyroid dysfunction is a manageable irAE than can occur during breast cancer treatment. It is important to implement routine thyroid function monitoring as part of the clinical management of patients undergoing immunotherapy. With appropriate diagnosis and timely intervention, clinicians can effectively reduce the impact of thyroid dysfunction on the patient’s overall treatment protocol and quality of life.