Background Thyroid dysfunction is a well known side effect of immune checkpoint blockade (ICB) and is one of the most common causes of immune-related adverse events (IRAE).1–9 The incidence varies with each individual therapy but generally estimated to be in the range between 6–18% per one study. Hypothyroidism and thyroiditis are the most common manifestations. Initial hyperthyroidism followed by hypothyroidism is another manifestation. Hypothyroidism is more common with an incidence of 10% whereas hyperthyroidism has an incidence of 5%. Less is known about the incidence of worsening thyroid dysfunction in patients with pre-existing thyroid dysfunction treated with ICB.
Methods A retrospective analysis was collected on 370 patients who received immunotherapy from April 2015 to April 2019. Of those, 212 had abnormal thyroid function tests. We analyzed a subgroup of these patients who had baseline thyroid dysfunction for worsening thyroid dysfunction after they were given ICB. Fifty-three patients were included in the analysis and had an abnormal baseline TSH at the start of immunotherapy. Type of immunotherapy, worst TSH, duration between initiation of immunotherapy to worst TSH, treatment type, and grade of abnormality as per Immune Checkpoint Inhibitor Related Adverse Events Common Terminology Criteria for Adverse Events (IRAE-CTCAE) were also recorded. Analysis was done for patients to compare likelihood of worsening TSH resulting in change in treatment for thyroid disorder.
Results Of the identified patients (N=53) with abnormal TSH screening values outside of the institution’s normal reference range 0.35 - 4.95 uIU/ml, 45.7% (N=16) were hypothyroid and 54.3% (N=19) were hyperthyroid at baseline. Of those who were hypothyroid, 50% (N=8) had worsening TSH and 50% (N=8) had unchanged TSH during treatment. Of those who were hyperthyroid, 31.6% (N=6) had unchanged TSH, 52.6% (N=10) had worsened TSH, and 15.8% (N=3) had normalization of TSH compared to baseline. Overall 26.4% had worsening and of those 11.3% required treatment change.
Conclusions Thyroid dysfunction is one of the most common IRAE’s associated with immune checkpoint inhibitors. Little is known about the impact of immunotherapy on patients with existing thyroid dysfunction. Patients who have underlying thyroid dysfunction are at an increased risk for worsening thyroid dysfunction with the use of ICB but though not unduly above the risk general population. Of those with change, only a modest percentage required an alteration of their endocrine therapy. Of interest, our data suggests a potential increased risk in patients with baseline hyperthyroidism compared to hypothyroidism which may be clinically relevant.
Ethics Approval The study was approved by ECU Brody School of Medicine Institution’s Ethics Board, approval number 19-000710.
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