7120 Pituitary Prolactinoma Transforming To Invasive Aggressive Adenoma After 10 Years of Acting As Benign Adenoma

Abstract Disclosure: S.N. Polis: None. S. Nakhle: None. N.J. Vernetti: None. Prolactinomas are the most common type of secretory pituitary tumors. Symptoms occur due to hyperprolactinemia and compressive symptoms with larger tumors. The majority of the prolactinomas are benign adenomas, with up to 30-40% of them being invasive. Malignant prolactinomas are rare, counting only 0.2% of pituitary tumors with an average latency period of 4.7 years. We present a 70-year-old woman who was found to have asymptomatic mild hyperprolactinemia in 2009 with pituitary MRI that showed a 3 mm left pituitary adenoma. Treatment with cabergoline started three years later due to an increase in prolactin above 300 ng/ml. Annual pituitary MRI showed a stable mass. After four years of treatment, pituitary MRI showed an increase in pituitary adenoma size to 8 mm and prolactin level remained elevated above 300 ng/ml. The patient complained of facial and acral numbness and emotional outbursts, so cabergoline was changed to bromocriptine. A few months later, a decision was made to stop treatment as she was asymptomatic and prolactin levels remained stable with a stable adenoma on imaging. 18 months later, prolactin increased to 544 ng/ml and pituitary MRI showed an increase adenoma size to 14mm, contacting the chiasm, and cabergoline was restarted. The prolactin levels continued to climb after 5 months of treatment despite titrating the dose to 1 mg daily. The patient started to develop vision impairment and visual field testing confirmed a new central vision defect. The patient was eventually referred to neurosurgery and went for transsphenoidal surgery. Prolactin level dropped to 50 ng/ml post operatively. The pathology report showed Ki 67 10-20%. Cabergoline was restarted and the patient was enrolled in a clinical trial for temozolomide for 18 months. During that time, prolactin levels remained stable so treatment was discontinued. A year later, cabergoline was restarted as prolactin levels increased to 219 ng/ml and pituitary MRI showed an 8 mm sellar mass with optic chiasm compression. For the next year, multiple medical treatments including high dose cabergoline (1 mg daily) and temozolomide were attempted, which were intolerable due to side effects. Prolactin continued to climb (> 1700 ng/ml). Four years later, the patient went for a second transsphenoidal surgery. Surgical pathology revealed Ki67 20%. Prolactin levels dropped to 242 ng/ml, but a month later, went up again to over 600 ng/ml. Cabergoline was restarted with a plan for an open craniotomy and radiotherapy. Conclusion: We present this interesting case of pituitary prolactinoma that behaved as benign adenoma for over 10 years prior to invasion and showing aggressive behavior requiring multiple surgeries. This unusual presentation is worrisome for malignancy and prompting consideration for closer and longer follow up for prolactinomas, especially the ones resistant to medical treatment. Presentation: 6/2/2024