SUN-430 An Unusual Presentation of Hypopituitarism in the Setting of Metastatic Breast Carcinoma: A Case Report

Introduction: Metastasis to the pituitary gland (PM) are infrequent (1). Breast and lung cancer are the most common primary cancer of PM. We report an interesting case of metastatic breast cancer with pituitary gland involvement debuting with diabetes insipidus as the initial symptom. Clinical Case: A 59-year-old woman presented with symptoms of polydipsia, polyuria, unquantifiable weight loss, and generalized body weakness. Initial assessment showed evidence of panhypopituitarism as per: FT4 0.39 (0.60-1.32 ng/dL), TSH 1.39 (0.45-5.33 uIU/mL), Cortisol 1.8 (6.7-22.6 ug/dL), ACTH 13 (6-50 pg/mL), Prolactin 223.5 (2.74-19.64 ng/mL), Estradiol 222 (<= 31 pg/mL) while on estradiol pellets, LH 0.2 (10.87-58.64 mIU/mL), FSH 1.6 (16.74-113.59 mIU/mL), Na 146 mmol/L, Cl 112 mmol/L, and urine specific gravity 1.004. MRI of the brain reported a pituitary macroadenoma measuring 1.0x1.6x1.8 cm, extending posteriorly along the infundibulum. She was initially treated with hydrocortisone, levothyroxine, cabergoline, and desmopressin. Physical examination was remarkable for a right breast lump. Breast ultrasound showed a mass measuring 1.2x1.2 cm. A biopsy was performed reporting invasive lobular carcinoma, Nottingham histologic grade 2 [ER (85%) PR (61%) and HER2 negative with a KI67 of 2%]. Posteriorly, the patient underwent pituitary biopsy and trans sphenoidal resection with pathology report of metastatic breast carcinoma [ER 20% PR 2% HER2 negative by FISH]. Pituitary stains were negative for prolactin.Subsequent breast cancer staging with CT Abdomen/pelvis and 18F-FDG PET/CT revealed widely metastatic disease including right and left breast, bilateral axillary LAD, moderate bilateral hydronephrosis, and extensive bone disease in the axial and appendicular skeleton. Patient has been treated with 15 cycles of whole-brain radiation therapy, and the current treatment approach is no longer curative, focused on palliative chemotherapy and hormonal replacement therapy. Prolactin levels have normalized. Conclusion: Our case remarks the importance of working up pituitary macroadenomas with diabetes insipidus. Even though metastatic pituitary tumors are rare, awareness of clinical presentation is essential to keep in our differential that isolated pituitary tumors can be an initial presentation of the metastatic process, allowing early diagnosis and interventions. Keywords: Hypopituitarism, Pituitary Gland, Pituitary Metastasis References: 1. Javanbakht A, D'Apuzzo M, Badie B, Salehian B. Pituitary metastasis: a rare condition. Endocr Connect. 2018 Aug 23. pii: EC-18-0338. doi: 10.1530/EC-18-0338.