Immunotherapy-Induced Thyroiditis in Cancer Patients

Abstract

Hyperthyroid patients may have increased or decreased radioiodine uptake on I-123 uptake and scan, which helps to differentiate the etiology of the hyperthyroid state. Thyroiditis is an uncommon complication of cancer immunotherapy and, in this situation, is likely secondary to an autoimmune response. The typical presentation of thyroiditis, regardless of the etiology, is elevated T4 and/or T3, low TSH and low radioactive iodine uptake. Herein we report a case of cancer immunotherapy-induced thyroiditis in a 34-year-old female diagnosed with right breast grade 2 invasive ductal carcinoma with ER and PR positive, Her2neu negative tumor markers. Due to her ER-positive tumor, 8-cycles of chemo-immunotherapy with Paclitaxel + Pembrolizumab were prescribed. The patient began to complain of intermittent palpitations halfway through her treatment, and her TSH after 6 cycles of treatment was <0.01 U/ml. She had negative TSI or anti-TPO (Pre-treatment TSH- 1.54 U/ml) antibodies. I-123 thyroid uptake and scan demonstrated faint thyroid activity with very low I-123 uptake, consistent with thyroiditis. Her treatment was ultimately continued and continued close monitoring of thyroid function tests was recommended.