SUN-923 Combination Immune Checkpoint Inhibitor Therapy for ACTH-Secreting Pituitary Carcinoma

Introduction Pituitary carcinoma is a rare yet serious entity with poor prognosis despite multimodal therapies. Cerebrospinal and/or systemic metastases are present by definition, making adjuvant systemic therapy necessary. Novel treatments are urgently needed for refractory cases. Immunotherapy with immune checkpoint inhibitors (ICI) targeting cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed cell death 1 (PD-1) or its ligand (PD-L1) has been a revolution in multiple malignancies. The expression of CTLA-4 and PD-L1 has been elucidated in pituitary adenomas and could be implicated in pituitary carcinomas as well. Hypophysitis is also a frequent endocrine immune-related adverse event, especially during CTLA-4 blockade (with ipilimumab) or combination ICI. However, the efficacy of ICI in the treatment of refractory pituitary tumors has yet to be established. In 2018, Lin et al. successfully treated a first case of a hypermutated aggressive ACTH-secreting pituitary carcinoma with ipilimumab (anti-CTLA-4) and nivolumab (anti-PD-1) combination immunotherapy. Clinical Case We report a 40-year old male, diagnosed with an invasive ACTH-secreting pituitary macroadenoma in 2012, initially treated by transsphenoidal and transcranial surgery, followed by adjuvant stereotactic radiotherapy and several courses of ketoconazole. In 2017, he presented to our clinic for a recurrent Cushing’s phenotype despite maximal dosing of ketoconazole. Therapy both with pasireotide and cabergoline was unable to normalize cortisol levels and a bilateral (subtotal) adrenalectomy was performed. In June 2018, he presented to our emergency department with acute diplopia due to a left abducens nerve palsy. Imaging revealed recurrent invasion of the tumor into the sella turcica and cavernous sinus, together with cerebellar and drop metastases at the cervical spine. Temozolomide (TMZ) was initiated for a total of 9 cycles. Progressive disease was observed with development of new onset right oculomotor nerve palsy after the last TMZ cycle, and persistence of elevated serum ACTH-cortisol and urinary cortisol levels, despite the absence of radiological progression. Therefore, he was started in a compassionate use setting with a combination ICI therapy with ipilimumab 3 mg/kg and nivolumab 1 mg/kg (for 4 cycles), followed by maintenance nivolumab therapy (240 mg) every two weeks. He has stable disease (both radiographically and hormonally) five months after the initiation of the immunotherapy. Clinical Lesson(s) or Conclusion(s) We report the second case of ACTH-secreting pituitary carcinoma treated with combination ICI therapy. The disease status of the patient is stable up until now, suggesting at least disease control by the immunotherapy. Checkpoint blockade inhibitors are a promising novel treatment modality for refractory pituitary tumors and should be further studied.