FRI306 Natural History Of Untreated Prolactinoma

Disclosure: M. Sadek: None. N. Sandila: None. D.B. Clarke: None. S.A. Imran: None. BACKGROUND Prolactinomas (PRLomas) are the most common functioning pituitary tumors, and the majority are microPRLomas (<10 mm in size). Current guidelines do not support treating asymptomatic or minimally symptomatic microPRLomas based on older studies utilizing insensitive imaging and assay techniques, whereas only limited information is available about the natural history of microPRLomas based on new generation assay and advanced imaging modalities. OBJECTIVES This study aims to assess the natural history of medically untreated microPRLomas with regards to long-term trends of serum PRL, tumor growth, clinical symptoms, and their effect on other pituitary function. METHODS We conducted a retrospective review of all patients diagnosed with microPRLoma since 2005 from our comprehensive provincial pituitary registry in Nova Scotia, Canada. Secondary causes of hyperprolactinemia were excluded. Outcomes were extracted at diagnosis and each follow-up visit. PRL, % above upper limit of normal (AULN) and tumor size (mm) were modelled using linear mixed effects models and clinical symptoms were analyzed with McNemar’s Test. Increase in PRL was modeled with exact logistic regression with change in tumor size and symptoms as predictors. RESULTS A total of 28 patients were identified; median age at diagnosis was 37 yrs (IQR 27.5 - 47.5) and median follow-up was 70 months (IQR 41.5 - 123.5). No patient had additional pituitary hormonal abnormality except gonadal dysfunction. Median tumour size at diagnosis was 3 mm (IQR 2 - 4), and median PRL (AULN) was 50% (IQR 15.2 - 113.3). Twenty four (85.7%) had symptoms at diagnosis including: galactorrhea, oligomenorrhea and amenorrhea. At last follow-up, those without symptoms at diagnosis remained asymptomatic and the majority (80%) with symptoms at presentation had complete resolution of symptoms (p<0.01). Only 20% had persistent symptoms, commonest being galactorrhea, but none had worsening of symptoms. There was no evidence of any association between elevated serum prolactin and persistent symptoms. Overall, mean change in tumor size (mm) was -0.9286 (p-value = 0.0138), of which, 2 patients (7%) had an increase since diagnosis (mean increase = 2.5 mm) while the rest (93%) had either no change or a decrease in tumor size. Serum PRL (AULN) when adjusted for change over time (month) over during the entire follow-up period decreased in 20 (71.4%) patients by a median of -0.00793 (IQR -0.01556 - -0.00597) and increased in 8 (28.6%) by a median of 0.00321 (IQR 0.00181 - 0.01549).CONCLUSIONS Although limited by sample size, these findings suggest that when left untreated, the majority of microPRLomas remain stable both in terms of size and PRL values and clinical symptoms resolve in most patients over time. Presentation: Friday, June 16, 2023