Immune checkpoint inhibitor-related hypophysitis and endocrine dysfunction: clinical review

Immune checkpoint inhibitors are a new and effective class of cancer therapy, with ipilimumab being the most established drug in this category. The drugs' mechanism of action includes promoting the effector T cell response to tumours and therefore increased autoimmunity is a predictable side effect. The endocrine effects of these drugs include hypophysitis and thyroid dysfunction, with rare reports of adrenalitis. The overall incidence of hypophysitis with these medications is up to 9%. Primary thyroid dysfunction occurs in up to 15% of patients, with adrenalitis reported in approximately 1%. The mean onset of endocrine side effects is 9 weeks after initiation (range 5-36 weeks). Investigation and/or screening for hypophysitis requires biochemical and radiological assessment. Hypopituitarism is treated with replacement doses of deficient hormones. Since the endocrine effects of immune checkpoint inhibitors are classed as toxic adverse events, most authors recommend both discontinuation of the immune checkpoint inhibiting medication and 'high-dose' glucocorticoid treatment. However, this has been challenged by some authors, particularly if the endocrine effects can be managed (e.g. pituitary hormone deficiency), and the therapy is proving effective as an anticancer agent. This review describes the mechanism of action of immune checkpoint inhibitors and details the key clinical endocrine-related consequences of this novel class of immunotherapies.