Combined PD-1 and CTLA-4 Blockade Increases the Risks of Multiple Pituitary Hormone Deficiency and Isolated Adrenocorticotropic Deficiency: A Prospective Study

Background: Anti-cytotoxic T-lymphocyte antigen-4 antibody (CTLA-4-Ab) monotherapy induces two types of pituitary immunerelated adverse events (irAEs): multiple pituitary hormone deficiency (Multi-D; impairment of ≥2 anterior pituitary hormones) and isolated adrenocorticotropic hormone (ACTH) deficiency (IAD). Combination therapy with CTLA-4-Ab and anti-programmed cell death-1 antibody (PD-1/CTLA-4-Abs), which is increasingly replacing CTLA-4-Ab monotherapy, frequently causes pituitary irAEs; however, whether it increases Multi-D/IAD incidence is unknown. Methods: In total, 74 and 748 patients with malignancies treated with PD-1/CTLA-4-Abs and PD-1-Ab, respectively, were prospectively evaluated for ACTH and cortisol levels at baseline and every 6 weeks after treatment initiation, and then observed until the last clinical visit. The characteristics of pituitary irAEs were evaluated by pituitary stimulation tests and compared with those induced by PD-1-Ab monotherapy. Results: PD-1/CTLA-4-Abs therapy showed higher incidence rates of pituitary irAEs (16/74 [21.6%] vs. 25/748 [3.3%], P<0.001), Multi-D (9/74 [12.2%] vs. 2/748 [0.3%], P<0.001), and IAD (7/74 [9.5%] vs. 23/748 [3.1%], P=0.014) than PD-1-Ab monotherapy. ACTH deficiency was observed in all cases, whereas the prevalence rates of luteinizing hormone deficiency (8/16 [50.0%] vs. 1/25 [4.0%]), follicle-stimulating hormone deficiency (6/16 [37.5%] vs. 1/25 [4.0%]), and thyrotropin deficiency (4/16 [25.0%] vs. 0/25 [0%]) were significantly higher after PD-1/CTLA-4-Abs than after PD-1-Ab treatment. Pituitary enlargement, which was observed only in the Multi-D cases, was significantly more frequent after PD-1/CTLA-4-Abs than after PD-1-Ab treatment (6/16 [37.5%] vs. 0/25 [0%], P=0.002). Conclusion: This prospective study revealed high risks of both Multi-D and IAD under PD-1/CTLA-4-Abs treatment, emphasizing the need for careful evaluation of pituitary function.