Meet the Professor 8

22 Mar 2026 13:30 14:00

201DE

Pituitary

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Time	Session

13:30 14:00	Hypophysitis: Difficult Cases Yutaka TakahashiJapan Speaker Paraneoplastic Autoimmune Hypophysitis: A Novel Form Paraneoplastic Endocrine SyndromeThe story begins with a fascinating case we encountered in 2003. It was an outlier of hypopituitarism that presented with acquired deficiencies in GH, PRL, and TSH. We subsequently accumulated similar cases and reported them as a novel disease entity named "anti-PIT-1 hypophysitis." We clarified that this condition represents a paraneoplastic syndrome associated with thymoma or malignancies. The mechanism of onset involves ectopic expression of PIT-1 in the tumor, leading to a breakdown of immune tolerance. As a result, anti-PIT-1 antibodies are produced in the blood, and PIT-1–expressing cells (those producing GH, PRL, and TSH) in the pituitary are damaged by cytotoxic T lymphocytes (CTLs). Recently, we have succeeded in establishing a disease model using co-culture of CTLs and patient-derived iPS cell–generated pituitary cells, demonstrating that CTLs are indeed the causatively involved. Interestingly, we found that a similar mechanism underlies some cases of isolated ACTH deficiency and immune checkpoint inhibitor–related hypophysitis (PD-1/PDL-1-related hypophysitis). Based on this, we proposed a broader new disease concept: “paraneoplastic autoimmune hypophysitis.” Very recently, we discovered a case of “immune checkpoint inhibitor–related anti–PIT-1 hypophysitis,” which clearly supports this concept. To elucidate the pathophysiology of such novel diseases, we emphasize the importance of a cross-disciplinary academic framework—beyond organ-specific medical practice and beyond endocrinology alone—which we refer to as "onco-immuno-endocrinology." In this lecture, I will introduce our research journey and share key insights and lessons for young physician-scientists aiming to reshape the textbooks of the future.Hypophysitis: Difficult CasesHypophysitis is defined as inflammation of the hypothalamo-pituitary region and is classified into primary and secondary forms. Primary hypophysitis refers to autoimmune hypophysitis (lymphocytic hypophysitis) and is essentially a diagnosis by exclusion of other diseases. Secondary hypophysitis can be classified into those associated with local lesions, systemic diseases, or drug-induced causes. Therefore, differential diagnosis from other conditions presenting with similar findings is crucial. Among the secondary forms, immune checkpoint inhibitor–related hypophysitis has emerged. In addition, the newly proposed entity paraneoplastic autoimmune hypophysitis have recently drawn considerable attention. That includes anti-PIT-1 hypophysitis, a component of isolated ACTH deficiency and PD-1/PDL-1-related hypophysitis, in which common mechanism underlies. Ectopic expression of pituitary antigens such as POMC and PIT-1 causes breakdown of immune tolerance and specific cytotoxic T cells injure anterior pituitary cells, results in a specific defect in ACTH or GH, PRL, and TSH, respectively. For systemic diseases, diagnosis proceeds by examining specific disease markers and searching for involvement of other organs. On the other hand, it is often difficult to differentiate lesions confined to the hypothalamo-pituitary region. In atypical cases, pituitary biopsy should be considered. When performing a biopsy, appropriate selection of the biopsy site is essential. If possible, the decision should be made before administering pharmacologic doses of glucocorticoids. In this Meet the Professor session, I would like to provide up-to-date information and foster discussion with audience on key points in the differential diagnosis of hypophysitis, with a focus on immune checkpoint inhibitor–related hypophysitis and paraneoplastic autoimmune hypophysitis, which represent emerging disease concepts. 201DE

Time

Session

13:30

14:00

Hypophysitis: Difficult Cases

Yutaka TakahashiJapan Speaker Paraneoplastic Autoimmune Hypophysitis: A Novel Form Paraneoplastic Endocrine SyndromeThe story begins with a fascinating case we encountered in 2003. It was an outlier of hypopituitarism that presented with acquired deficiencies in GH, PRL, and TSH. We subsequently accumulated similar cases and reported them as a novel disease entity named "anti-PIT-1 hypophysitis." We clarified that this condition represents a paraneoplastic syndrome associated with thymoma or malignancies. The mechanism of onset involves ectopic expression of PIT-1 in the tumor, leading to a breakdown of immune tolerance. As a result, anti-PIT-1 antibodies are produced in the blood, and PIT-1–expressing cells (those producing GH, PRL, and TSH) in the pituitary are damaged by cytotoxic T lymphocytes (CTLs). Recently, we have succeeded in establishing a disease model using co-culture of CTLs and patient-derived iPS cell–generated pituitary cells, demonstrating that CTLs are indeed the causatively involved. Interestingly, we found that a similar mechanism underlies some cases of isolated ACTH deficiency and immune checkpoint inhibitor–related hypophysitis (PD-1/PDL-1-related hypophysitis). Based on this, we proposed a broader new disease concept: “paraneoplastic autoimmune hypophysitis.” Very recently, we discovered a case of “immune checkpoint inhibitor–related anti–PIT-1 hypophysitis,” which clearly supports this concept. To elucidate the pathophysiology of such novel diseases, we emphasize the importance of a cross-disciplinary academic framework—beyond organ-specific medical practice and beyond endocrinology alone—which we refer to as "onco-immuno-endocrinology." In this lecture, I will introduce our research journey and share key insights and lessons for young physician-scientists aiming to reshape the textbooks of the future.Hypophysitis: Difficult CasesHypophysitis is defined as inflammation of the hypothalamo-pituitary region and is classified into primary and secondary forms. Primary hypophysitis refers to autoimmune hypophysitis (lymphocytic hypophysitis) and is essentially a diagnosis by exclusion of other diseases. Secondary hypophysitis can be classified into those associated with local lesions, systemic diseases, or drug-induced causes. Therefore, differential diagnosis from other conditions presenting with similar findings is crucial. Among the secondary forms, immune checkpoint inhibitor–related hypophysitis has emerged. In addition, the newly proposed entity paraneoplastic autoimmune hypophysitis have recently drawn considerable attention. That includes anti-PIT-1 hypophysitis, a component of isolated ACTH deficiency and PD-1/PDL-1-related hypophysitis, in which common mechanism underlies. Ectopic expression of pituitary antigens such as POMC and PIT-1 causes breakdown of immune tolerance and specific cytotoxic T cells injure anterior pituitary cells, results in a specific defect in ACTH or GH, PRL, and TSH, respectively. For systemic diseases, diagnosis proceeds by examining specific disease markers and searching for involvement of other organs. On the other hand, it is often difficult to differentiate lesions confined to the hypothalamo-pituitary region. In atypical cases, pituitary biopsy should be considered. When performing a biopsy, appropriate selection of the biopsy site is essential. If possible, the decision should be made before administering pharmacologic doses of glucocorticoids. In this Meet the Professor session, I would like to provide up-to-date information and foster discussion with audience on key points in the differential diagnosis of hypophysitis, with a focus on immune checkpoint inhibitor–related hypophysitis and paraneoplastic autoimmune hypophysitis, which represent emerging disease concepts.

201DE