Multimodal management of giant prolactinoma with extensive amyloid spherule deposition: a case report with review of the literature.

Amyloid spherule-containing prolactinomas are rare entities associated with dopamine agonist (DA) resistance and aggressive behaviour. We report a giant amyloid spherule-containing prolactinoma with a substantial tumour burden and markedly elevated prolactin levels, highlighting novel multimodal therapeutic strategies. A 49-year-old man presented with headache and visual disturbance. Imaging revealed a giant pituitary macroadenoma (63 × 84 × 46 mm) with Knosp grade 4 cavernous sinus invasion and clivus erosion. Laboratory investigations revealed marked hyperprolactinemia (prolactin (PRL): 30,969 ng/mL) and autonomous growth hormone (GH) hypersecretion. Histopathology confirmed a sparsely granulated lactotroph tumour with extensive amyloid spherules and dystrophic calcifications (Ki-67: 8%). Notably, immunohistochemistry demonstrated PRL positivity without GH immunoreactivity, suggesting tumour heterogeneity with sampling limitations. Comprehensive systemic amyloidosis screening, the first systematic evaluation reported for this entity, excluded systemic disease. Following surgical debulking with extensive residual disease, postoperative cabergoline treatment resulted in a reduction in the PRL (4,700→927 ng/mL). Given the presence of amyloid-associated dopamine resistance, cabergoline was discontinued, and radiotherapy (RT) (45 Gy) was initiated to control the amyloid burden, followed by temozolomide. Based on evidence from other malignancies suggesting RT-mediated amyloid reduction, cabergoline was reintroduced postradiotherapy without paradoxical tumour growth. Concurrent cabergoline-temozolomide therapy, a novel approach that differs from conventional sequential protocols, achieved a dramatic response: 93.4% prolactin reduction (10,320→677 ng/mL) and 52.4% tumour volume reduction. This superior outcome far exceeded that of initial postsurgical cabergoline monotherapy (80% reduction), suggesting that RT successfully modulated the amyloid burden and restored dopamine sensitivity. This case suggests that RT may restore dopamine agonist sensitivity in patients with amyloid-containing prolactinomas, potentially enabling concurrent dopamine agonist-temozolomide therapy in refractory cases, warranting further validation.