Pasireotide: A potential therapeutic alternative for resistant prolactinoma

Context: About 10% of prolactinomas are resistant to dopamine-agonists (DAs). The only alternatives for tumor and prolactin control are surgery or radiotherapy. While studies on first generation somatostatin analogs have shown no efficacy against prolactinomas, no study has been conducted on the new multireceptor-targeted somatostatin receptor ligand pasireotide, which presents high affinity for 5, 3, 2 and 1 receptor subtypes.

Case description: A 41 year-old woman presented with a macroprolactinoma showing resistance to all available DAs. She was first diagnosed at 17 years old after which she had undergone two incomplete debulking surgeries. Under pasireotide long-acting release (LAR) treatment, plasma prolactin levels normalized and symptoms disappeared within one month after initiation. The clinical benefits of the monotherapy (specifically, prolactin levels within normal range and stable tumor volume) were maintained for seven years. Glucose tolerance was satisfactory. Pathological analysis of the tumor revealed high SSTR5 and low SSTR2 expression (25 and 5% of cells respectively).

Conclusion: This is a promising first report of a patient with a DA-resistant macroprolactinoma who achieved long-term control, in terms of prolactin normalization and tumor volume, under pasireotide treatment alone. Pasireotide could thus be an alternative in prolactinomas resistant to DA. SSTR expression analysis on pathology could guide patient selection.