[Background] Immune checkpoint inhibitor (ICI)-related hypophysitis (RH) is a common immune-related adverse event. The early detection of ICI-RH prevents life-threatening adrenal insufficiency. However, good predictors of secondary adrenal insufficiency in ICI-RH have not yet been reported. We hypothesized that fluctuations in serum adrenocorticotropic hormone (ACTH) and cortisol levels occur similarly to those in thyroid-stimulating hormone and thyroid hormones (thyroxine and triiodothyronine) in ICI-related thyroiditis. Here, we sought to test this hypothesis. [Methods] Patients who used ICI and had a history of measurement of serum ACTH and cortisol concentrations were retrieved from electronic medical records, and those with a history of glucocorticoid use were excluded from the analysis. We evaluated fluctuations in serum ACTH and cortisol concentrations and the development of ICI-RH. For patients with ICI-RH, data at three points (before ICI administration [pre], maximum ACTH concentration [peak], and onset of ICI-RH) were analyzed to evaluate hormone fluctuations. [Results] A total of 202 patients were retrieved from the medical record. Forty-three patients were diagnosed with ICI-RH. Twenty-six out of 43 patients had sufficient data to evaluate fluctuations in serum ACTH and cortisol concentrations and no history of glucocorticoid use. ACTH concentrations changed from 37.4 [29.9-48.3] (pre) to 64.4 [46.5-106.2] pg/mL (peak) (1.72-fold increase, p = 0.0026) in the patients with ICI-RH before the onset. There were no differences in cortisol concentrations between the pre and peak values in patients with ICI-RH. We also evaluated the fluctuations in serum ACTH and cortisol levels in patients who did not receive ICI-RH (62 cases). However, elevation of serum ACTH levels was not observed in patients without ICI-RH, suggesting that transient elevation of serum ACTH is a unique phenomenon in patients with ICI-RH. [Conclusions] Serum ACTH levels were transiently elevated in some patients with ICI-RH before the onset of secondary adrenal insufficiency. Monitoring the ACTH levels and their fluctuations can help predict the onset of ICI-RH.

The authors have declared no competing interest.

KAKENHI(grant numbers 21K16370 and 21KK0149 [HB]) and Takeda Science Foundation (Medical Research Grant [HB]).

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Ethics committee of Kobe University Graduate School of Medicine gave ethical approval for this work.

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