Somatic Activating ESR1 Mutation in an Aggressive Prolactinoma.

Context and objective: The genetic profile of prolactinomas remains poorly understood. Our objective is to identify somatic genetic alterations associated with prolactinomas and to report the identification of an activating ESR1 mutation (ESR1Y537S) in an aggressive prolactinoma.

Setting: Brigham and Women's Hospital.

Design: Massively parallel-sequencing panel (OncoPanel) was performed in a cohort of patients with prolactinomas to identify mutations and copy number variation (CNV).

Results: Twenty subjects (mean age 38.6 years; 12 women and 8 men) were included in this study. A somatic ESR1Y537S mutation was identified in an aggressive prolactinoma in a post-menopausal woman. No SF3B1 or other somatic mutations were identified. The median number of CNV events identified in our samples was 46; the prolactinoma with ESR1Y537S had the highest number with 233 events. In breast cancer, ESR1Y537S has been shown to activate estrogen receptor alpha independent of ligand binding. In patients with resistant breast cancer and ESR1Y537S, elacestrant, a second-line ER degrader, improves progression-free survival. Therefore, given the lack of response to multimodality therapies, elacestrant was initiated in this patient after the third cycle of radiotherapy. Elacestrant, along with radiotherapy, controlled tumor growth and significantly reduced prolactin levels.

Conclusion: Molecular profiling allowed the identification of ESR1Y537S, in an aggressive prolactinoma. ESR1Y537S was not detected early in the course of the disease and is likely conferring tumor aggressiveness. This finding emphasizes the significance of estrogen receptor signaling in prolactinomas. It also allowed the use of targeted therapy with successful control of disease progression.