OR32-02 Immune Checkpoint Inhibitor-Induced Hypophysitis Is Associated with Improved Overall Survival in Cancer Patients

Context: Immune checkpoint inhibitors (ICIs) are monoclonal antibodies against checkpoints namely CTLA-4, PD-1 and PD-L1. These can cause pituitary dysfunction due to hypophysitis in addition to other endocrinopathies. While the prevalence and course of hypophysitis have been described extensively, the relationship between hypophysitis and cancer prognosis has only been investigated in melanoma patients on ipilimumab. Additionally, the impact of high dose glucocorticoids for hypophysitis treatment on survival has been unclear. Objective: In order to address these important questions, we aimed to characterize the frequency and course of hypophysitis from various ICIs, and to investigate a possible impact on overall survival in cancer patients.Design and Methods: We conducted a single center retrospective cohort study of adult cancer patients that received an ICI from 1/1/2012 - 12/31/2016, followed for a median of 14.8 months. A total of 896 patients were identified that received ipilimumab alone (n=120); ipilimumab and nivolumab (n=50); ipilimumab followed or preceded by pembrolizumab (n=70), pembrolizumab alone (n=406), and nivolumab alone (n=250). Results: Twenty-six patients (2.9%) developed hypophysitis after a median of 2.3 months (range 0.8 to 11.7). Their median age at initiation of ICI was 57.9 years (range 42.4 to 78.5), 54% were males, and the most common malignancy was melanoma (81%). All had hypopituitarism showing secondary adrenal insufficiency (100%), central hypothyroidism (38.5%) and central hypogonadism (28.5% in men, 25% in premenopausal women). Sixty-four percent demonstrated pituitary enlargement on imaging which resolved on follow-up. Mass effects occurred in 50% and were managed by initial high dose glucocorticoids. Thyroiditis occurred in 19.2% of those with hypophysitis. Occurrence of hypophysitis was associated with better overall survival (median 50.7 vs 16.5 months; p value 0.015) and reduced mortality (RR 0.52, 95% CI 0.28 to 0.99; p value 0.036) after adjusting for age, sex and malignancy type. Conclusions: Hypophysitis, usually but not always accompanied by classic MRI features, occurrs within a few weeks in cancer patients most frequently after ipilimumab alone or in combination with a PD-1 inhibitor, rarely after pembrolizumab and never after nivolumab alone. ICI-induced hypophysitis presents as mass effects in half and as hypopituitarism in all patients involving the corticotrophs more commonly than thyrotrophs and gonadotrophs. The improved survival with a 48% lower mortality rate in patients with hypophysitis suggests its possible role as a marker for better efficacy of ICIs against malignancy.