The novel concept of "Onco-Immuno-Endocrinology" led to the discovery of new clinical entity "paraneoplastic autoimmune hypophysitis".

Recent advances in tumor immunology have enabled to develop immune checkpoint inhibitors and to save many patients with advanced cancer. Various endocrine diseases are caused by autoimmune mechanisms; it is important to understand that many endocrine organs are targeted by autoimmunity. In addition, some of malignant tumors ectopically produce hormones and lead to a clinically relevant ectopic hormone syndrome as an endocrine paraneoplastic syndrome. Thus, interplay between oncology, immunology, and endocrinology is important. We have defined a new clinical entity "paraneoplastic autoimmune hypophysitis" as "hypophysitis associated with autoimmunity against pituitary antigens caused by an ectopic expression of these antigens in the tumor and resulting in a breakdown of immune tolerance". To understand the pathophysiology of paraneoplastic autoimmune hypophysitis requires a fusion of the fields of oncology, immunology, and endocrinology; therefore, I propose a new concept of Onco-Immuno-Endocrinology.