A case of rapidly increasing cabergoline-resistant male prolactinoma

• Cabergoline is the first-line drug for treating male prolactinoma and resistant tumors are rare. • A rare case of male prolactinoma that recurred in a short period after tumor resection. • He required surgery and radiation therapy. • Combined therapy involving surgery and radiotherapy may be beneficial. Cabergoline, a dopamine agonist, is the first-line drug for treating prolactinoma. However, some rare cases exhibit resistance to cabergoline. Here, we report a rare case of prolactinoma in a male patient that recurred in a short period while the patient was undergoing cabergoline treatment following tumor resection. A 50-year-old man was diagnosed with a pituitary tumor (Knosp grade 3) and presented with symptoms of decreased libido, erectile dysfunction, and bilateral hemianopia. He underwent endoscopic transnasal pituitary tumor resection. The pathological diagnosis was prolactinoma. The intrasellar tumor was excised, except around the bilateral cavernous sinus, improving the patient’s visual dysfunction. However, despite postoperative treatment with cabergoline, the residual tumor rapidly enlarged, and the bilateral hemianopia recurred. The second tumor resection was performed 15 months after the initial surgery. The patient’s visual field loss once more improved, and postoperative oral cabergoline treatment was resumed. However, radiation therapy was required because the residual tumor in the cavernous sinus grew back. Since then, the patient’s condition has remained stable, and the tumor did not enlarge. In this case, the patient consistently showed strong resistance to cabergoline and required surgery and radiation therapy due to early recurrence of tumor growth after the initial surgery. Combined therapy involving surgical resection and radiotherapy may be beneficial for male patients with cabergoline-resistant prolactinoma.