SAT-726 Nonstandard Hormonal Management of Gynecomastia and Bone Health in a BRCA2-Positive Male on Androgen Deprivation Therapy

Abstract Disclosure: S. Kang: None. A. Foster: None. R. Bier: None. Background: Androgen deprivation therapy (ADT) is a cornerstone of prostate cancer treatment but is associated with common adverse effects, including gynecomastia and osteoporosis. Standard management includes tamoxifen or prophylactic radiotherapy for gynecomastia and antiresorptive agents for bone protection. The use of dopamine agonists or estrogen in this setting is rarely reported, especially in the context of long-term treatment. Data are also limited regarding the safety and effectiveness of these therapies in men with BRCA2 mutations. Clinical Case: A 77-year-old male with metastatic prostate cancer and a BRCA2 mutation was diagnosed in 1999 and has remained on continuous ADT since that time. Within a year of starting therapy, he developed progressive gynecomastia. To manage both breast enlargement and anticipated bone loss, he was started on transdermal estradiol (0.025 mg twice weekly) and cabergoline (0.5 mg three times weekly) - the former for skeletal protection, the latter to suppress further breast tissue growth despite normal prolactin levels. The patient has maintained this regimen for more than 20 years. Recent labs showed profoundly suppressed testosterone, LH, and FSH levels, low prolactin, and estradiol levels within the normal range for men. Notably, bone mineral density remained normal (T-scores: 1.2 spine, 0.4-0.8 hip, 0.0 femoral neck). However, the patient developed bilateral acetabular insufficiency fractures, with marrow edema and increased uptake seen on MRI and bone scan. Bone labs including calcium, phosphate, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, PTH, and alkaline phosphatase were all within normal limits. He has had no history of thromboembolic or cardiovascular events. Conclusion: This case illustrates the long-term use of nonstandard hormonal therapies in a BRCA2-positive male with metastatic prostate cancer on ADT. Cabergoline effectively stabilized gynecomastia in the absence of hyperprolactinemia, and estradiol patch therapy maintained normal bone density over decades. Yet, the development of insufficiency fractures highlights the complexity of fracture risk beyond bone density alone. This case underscores the importance of individualized management strategies in high-risk endocrine-oncology patients and invites further investigation into unconventional therapies when standard approaches are declined or unavailable. Presentation: Saturday, July 12, 2025