ODP361 A Case of Panhypopituitarism in the Setting of Metastatic Large Cell Neuroendocrine Carcinoma

INTRODUCTION: Metastasis to the pituitary gland is an uncommon cause of panhypopituitarism. The pituitary gland is an infrequent site overall for metastasis, with breast and lung cancer as most often found primary sites. Large cell neuroendocrine carcinoma is a rare form of lung cancer, and while metastasis to brain is not uncommon is this form of cancer, metastasis to the pituitary gland has rarely been reported. CLINICAL CASE: Patient was a 64 year old male with history of homelessness and substance use who had repeated hospitalizations for right sided pneumonia. Eventually bronchoscopy was performed, and tissue obtained via biopsy revealed a high-grade large cell neuroendocrine carcinoma. Initial brain imaging noted extensive brain metastases with numerous enhancing lesions in the cortex, as well as a 13×9×8 mm suprasellar mass abutting the optic chiasm. Thickening of the infundibulum was also noted. Lab testing demonstrated hypopituitarism with free thyroxine 0.52 (reference 0.93-1.7) ng/dL, thyroid-stimulating hormone 0.11 (2.7-4.2) ulU/mL, sodium 139 (135-147) mEq/L, total testosterone <0.1 (2.8-8) ng/ml, follicular-stimulating hormone 0.4 mlU/ml, lutenizing hormone <0.10 mlU/ml, prolactin 25.7 (4-15.2) ng/ml, cortisol <2 (3-12) ug/dL, and adrenocorticotropic hormone <5 (6-50) pg/mL. Diabetes insipidus was not present. Metastatic cancer was treated with dexamethasone and atezolizumab plus carboplatin and etoposide. Panhypopituitarism was treated with levothyroxine, testosterone replacement, and glucocorticoid replacement. One month later, patient represented with shortness of breath and headache. Repeat brain imaging showed an enhancing sellar mass measuring 21×15×11 mm extending superiorly to involve the pituitary stalk and hypothalamus. The extending suprasellar mass was noted to have enhancement and characteristics akin to remainder of brain metastases. The patient passed away from complications of metastatic carcinoma about three months after initial biopsy proven diagnosis. CONCLUSION: This patient developed extensive brain metastases from pulmonary large cell neuroendocrine carcinoma, which included a metastasis in the sella resulting in panhypopituitarism. While pituitary metastases from primary cancer are very rare events (with lung and breast carcinoma the most frequent sources), only a single case report exists describing a pituitary metastasis from a large cell neuroendocrine carcinoma. This case is also an important reminder to consider the pretreatment anatomy of the sella in patients subsequently exposed to immunomodulating chemotherapy, as a mass lesion seen during treatment may represent a preexisting metastasis rather than treatment-induced hypophysitis. Presentation: No date and time listed