MON-475 Discrepant Thyroid Function Tests in Adenocarcinoma-Is This a True Thyroid Disorder?

Background: Many causes of abnormal thyroid function tests (TFTs) occur that may or may not reflect a true thyroid disorder. The most common include: immune check point inhibitors therapies (ICI) used to treat various types of cancers; biotin supplements, which may interfere with thyroid function test assays; euthyroid sick syndrome; as well as amiodarone therapy for cardiac disorders. Clinical Case: A 67-year old female patient with type 2 diabetes mellitus, taking insulin and oral antihyperglycemic agents, with hyperlipidemia, hypertension and coronary artery disease, who had abnormal TFTs (TSH was 3.7 to 4.9 uIIu/ml; ref range 0.27-4.2 uIU/mL), and Free T4 was 0.92 to 1.06 ng/dL; ref range 0.55-1.6 ng/dl) prior to the diagnosis of metastatic adenocarcinoma of the lungs. She was initially treated with radiation. TFTs were unchanged. Her CEA was noted to be 129.5 (0-3.0 ng/mL). However, following chemotherapy with Tarceva (Erlotinib) 50 mg po daily, the TSH increased to 7.6 uIU/ml with Free T4 of 3.19 ng/dL. She remained clinically euthyroid. A thyroid ultrasound showed 1 -small sub centimeter nodule in each thyroid lobe. The patient later admitted to also taking biotin for an unknown period of time. TSH antibodies and TSI were both negative. Free T4 by dialysis was normal. While still taking Tarceva her TSH was noted to be 2.5 to 3.8 uIU/ml and both Free T4 and Free T3 were elevated and was 6.57 pg/ml;ref range=2.52-4.34 pg/mL). Six months later, the Free T4 decreased to 1.08 ng/dL. Thyroid antibodies and thyroglobulin remain normal. The patient remained clinically euthyroid. Conclusion: It is important to note that several factors can cause abnormal thyroid function tests, such as Immune check point inhibitors therapy, with the exact mechanism for abnormal TFTs unknown, and can also be associated with either Grave’s hyperthyroidism or Hashimoto’s hypothyroidism,as well as other autoimmune endocrine disorders. Biotin, a common supplement, has also been reported to interfere with the thyroid function test assays for free thyroxine (T4), total T4, free triiodothyronine (T3), total T3, TSH, and various cancer markers. However, It is important to clinically evaluate the patient for thyroid disorders, and recognize that therapy may not always be required, when discrepant and fluctuating thyroid function tests are obtained, such as in this patient. References: (1) Holmes EW, Samarasinghe S, Emanuele MA, Meah. Biotin interference in clinical immunoassays: a cause for concern. . Arch Pathol Lab Med. 2017;141:1459-1460. (2) Rossi E, Sgambato, De Chaira G, et al. Thyroid-induced toxicity of check-point inhibitors immunotherapy in the treatment of advance non-small cell lung cancer. J. Endocrinol Diabetes 2016;3:1-10.