PMON108 Metastatic Prostate Cancer Presenting as a Pituitary Macroadenoma: A Case Report

INTRODUCTION: Prostate cancer is the most common non-skin malignancy with an increasing incidence of distant stage spread. Prostate cancer is most frequently associated with skeletal, lymph node, and pulmonary metastases. Intracranial metastases are rare, occurring in only 0.4-0.6 percent of all cases. However, silent pituitary metastases are not uncommon in autopsy reports of cancer patients, with breast and lung cancer being the most common primary origin. Here we report a rare case of metastatic prostate adenocarcinoma that was originally thought to be a pituitary macroadenoma. CLINICAL CASE: A 57-year-old male with no known history of malignancy who presented with two weeks of headaches exacerbated by leaning forward. MRI showed a 2.8×2.8×2.7 cm sellar/suprasellar mass extending into the clivus and right sphenoid sinus favored to reflect a pituitary macroadenoma. He was found to have no visual, neurological, or endocrine abnormalities on exam, in addition to normal laboratory evaluation. He subsequently underwent transnasal resection of the mass and pathology revealed metastatic prostate cancer. Postoperative studies also revealed a significantly elevated prostate specific antigen (PSA) level of 383.8 ng/mL (normal range 0-4ng/mL) and a left posterolateral prostate mass extending into the left seminal vesicle, as well as multiple osseous metastases. In retrospect, he had been found to have an elevated PSA of 49.5 ng/mL five months prior which was thought to be secondary to infection but had not yet been repeated by his primary care provider. Fortunately, he had a favorable response to androgen deprivation therapy and Abiraterone/Prednisone. His PSA level decreased to <0.1 ng/mL and MRI showed complete resolution of the sellar/suprasellar mass while on androgen deprivation therapy. DISCUSSION: The rarity of pituitary metastases as well as lack of specific clinical and radiological features can make it difficult to differentiate from the much more common benign pituitary adenoma. Pituitary metastases are frequently asymptomatic or can present similarly to pituitary adenomas with headaches, visual changes, or hypopituitarism. Posterior pituitary metastases have been more frequently reported than anterior, thought to be due to the larger area of contact with the adjacent dura and direct blood flow from the systemic circulation. Rapid progression of size and symptoms, age greater than 50, and presence of diabetes insipidus should all raise suspicion for pituitary metastases, regardless of oncologic history, as the differentiation between malignant and benign is imperative in determining a therapeutic plan. The overall prognosis is poor in patients with prostate cancer metastatic to the brain, with a reported mean survival of 1-3 months in untreated cases and up to 14 months in those who underwent surgery or radiotherapy. CONCLUSION: This case reminds us of the importance of keeping malignant metastases in the differential diagnosis of sellar masses. Presentation: Monday, June 13, 2022 12:30 p.m. - 2:30 p.m.