Endocrine Abstracts

Background

The usage of Immune checkpoint inhibitors such as pembrolizumab grows over time due to their positive effect on survival and quality of life in patients with advanced cancer. The frequency of immune-related adverse events (IRAEs) associated with this drugs grows over time accordingly. Several endocrine-IRAEs of pembrolizumab are described in the literature and the thyroid disfunction is the most common.

Case description

A 55 year old man was referred to endocrinologist due to progressive fatique, memory troubles and 15 kg weight gain over past 3 months. His past medical history included a persistence of Graves disease for last 5 years after course of antithyroid drug treatment. Patient refused to undergo surgery or radioiodine treatment, so low dose methimazole was continued. One year ago patient was coincidentally found to have an advanced lung cancer: T4N3M1c, stage IVb. At the time of diagnosis patient was euthyroid on 5 mg of methimazole: TSH, free T4 and free T3 levels were 2.9 mIU/l, 12.8 (9.0–19.1) pmol/l and 5.6 (2.6–5.7) pmol/l respectively. The patient was given pembrolizumab (200 mg every 3 weeks) and was referred to endocrinologist with upper mention complaints when he had just received 11th cycle of pembrolizumab treatment. Thyroid function tests done after referral showed a TSH level of 112 mIU/l, free T4 level of 5.15 (9.0–19.1) pmol/l and free T3 level of 1.64 (2.6–5.7) pmol/l. The methimazole was stopped and replacement therapy with levothyroxine started. Six weeks later the patient reported a significant improvement in well-being. Three months later TSH level was 2.1 and fT4 level was 14.4 (9.0–19.1) pmol/l and current dose of 100 µg levothyroxine was continued.

Conclusion

Pembrolizumab treatment is associated with wide range of thyroid dysfunction which can shift from one form to another. This can misguide diagnosis and treatment process unless there is a high index of suspicion.