Emerging treatments
Novel somatostatin receptor 5 (SSTR5)-selective analogues
Prolactinomas express SSTR5 among the other recognised human SSTRs. Octreotide and lanreotide, the clinically available somatostatin analogues, bind poorly to SSTR5 and have proven to be ineffective for treatment of prolactinoma.[1] The novel somatostatin analogue pasireotide has a more universal SSTR binding profile, with improved binding affinity to SSTR1, SSTR2, SSTR3, and SSTR5. Pasireotide has achieved biochemical and tumour control in several case reports of patients with highly aggressive, dopamine agonist-resistant prolactinoma.[26][27] However, further studies are required to determine its role in treatment of prolactinoma.[28]
Temozolomide
Temozolomide is an alkylating agent that can be given orally and is used to treat patients with astrocytoma or glioblastoma. The effectiveness of temozolomide in reducing tumour size and serum prolactin in aggressive or malignant prolactinomas resistant to conventional therapies has been reported. The DNA repair enzyme O6-methyl-guanine-DNA methyltransferase (MGMT) protects tumour cells from alkylating agents. Prolactinomas with absent MGMT protein expression appear to be more likely to respond to temozolomide, although positive responses have also been observed in patients with prolactinomas that are MGMT-immunopositive.[29] Although results appear encouraging, data from these small case studies must be confirmed in larger, prospective clinical trials. Malignant or aggressive prolactinomas, particularly if resistant to dopamine agonists, may benefit from temozolamide (used off-label).[11][30]
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