High Dose Somatostatin Analogues in Neuroendocrine Tumors

Octreotide (OCT) is a somatostatin analogue (SSA) available in a long-acting formulation, conventionally administered every 28 days at the maximum dose of 30 mg. Together with lanreotide, it is considered the therapy of choice in the control of endocrine syndromes associated with neuroendocrine tumors (NET)s. A complete or partial clinical response to SSA therapy is generally achieved in at least 50% of the patients with neuroendocrine syndrome. Many studies reported a clinical response in 70-90% of functioning NETs. In about 36-50% of the patients with progressive advanced well differentiated NET (WDNET), a stabilization of disease occurs after treatment with subcutaneous OCT. By developing long-acting slow-release SSA formulation, long-acting OCT (LAR), lanreotide-SR, lanreotide-Autogel, the patient's compliance to SSA therapy was improved and escape from treatment, which was common with the subcutaneous formulation, was avoided. However, rate of objective response was not significantly improved as compared to short-acting SSA. On the other hand, it has to be remarked that long-acting SSA are being used in NET patients at doses correspondent to the low doses of short-acting formulation. The higher commercially available doses of LAR is 30 mg, which is assumed to be comparable to 300 µg of short-acting OCT in the therapy of acromegaly.

Only one study was designed to investigate the use of high-dose LAR (160 mg every 28 days). In this study, objective and hormonal responses in patients with progressive metastatic ileal NET non-responder to standard doses, was significantly elevated. However, this compound has never been commercialized and, of consequence, this first preliminary observation has not been confirmed by further studies.

No systematic studies were performed with the commercially available long-acting SSA used in high-dose treatments. In patients with progressive locally advanced or metastatic NET, increase of the dose or reduction of the interval between injections is a relatively common "empirical" clinical practice, but no studies have been performed to evaluate safety and efficacy of this treatment schedule.