Endocrine Abstracts

Introduction: In cancer patients treated with immune checkpoint-inhibitors (ICI) that target CTLA-4, PD-1 and/or PD-L-1, thyroid dysfunction represents the commonest associated endocrinopathy (1). Patients receiving ICI should be monitored for thyroid dysfunction. A case of PD-1 inhibitor-induced thyroid function test (TFT) interference has been reported (2) and having noted discordant results, we undertook a preliminary assessment of the extent of such ICI-related TFT interference in a cohort of our patients.

Methods: A quality improvement-project was conducted in a dedicated endocrine-immunotherapy clinic to investigate discordant TFT in patients receiving ICI. Discordant TFT results obtained locally by the Abbott Architect assays were reassessed by Beckman Coulter assays and Perkin-Elmer AutoDELFIA assays.

Results: Over an 8-month period, 3 male and 5 female patients were observed to have clinically discordant TFTs. The median age was 64 (IQR 55.5-82.5) years, and half (50%) of them had metastatic melanoma. All received PD-1 or PD-L-1 inhibitor therapy ± CTLA-4 inhibitors, with median treatment duration of 7 (IQR 4-30) months. All the patients had normal TFTs preceding ICI, with one patient being on levothyroxine replacement (LT4) for autoimmune primary hypothyroidism. Subsequently, 4 (50%) developed immunotherapy induced thyroiditis followed by hypothyroidism needing LT4, and 6 (75%) had other immunotherapy-related adverse reactions (rash, hypoadrenalism, hepatitis, colitis and polyarthritis). Upon routine TFT assessment using Abbott Architect assays, all had spuriously high free thyroid hormone (FT4) levels that were found to be normal when reanalyzed with Beckman Coulter assays or Perkin-Elmer AutoDELFIA assays, that were compatible with clinical thyroid status of all the patients except for one who had unexplained intermittent palpitations and heat intolerance.

Conclusions: Potential ICI therapy-induced interference in TFTs performed on some assay platforms is important. Clinicians should exercise caution when interpreting TFTs in patients receiving ICI, and should raise concerns with the laboratory in cases with discordant results.