The clinical management of neuroendocrine tumors with long-acting repeatable (LAR) octreotide: comparison with standard subcutaneous octreotide therapy.

Neuroendocrine tumors are rare, occurring in less than 1% of the population. They are divided clinically into functionally active or non-active tumors. Functionally active tumors produce a variety of substances (mainly peptides or serotonin) that are responsible for symptoms and sometimes can lead to the death of the patient independently from tumor proliferation. The most important compounds that can control symptoms in these patients are somatostatin analogs. Native somatostatin is not suitable for long-term clinical application due to its short half-life. Therefore, synthetic drugs were developed with improved pharmacokinetic characteristics. The best-characterized analog, octreotide, has been successfully applied to patients with functioning tumors. Octreotide can ameliorate symptoms in 30%-70% of the patients, mainly through a direct inhibitory effect on hormone production from the tumors. There is little or no effect on tumor growth during octreotide therapy; clinical responses were recorded in only 10%-30% of the patients. Recently, significant improvement in the management of the disease has been demonstrated with long-acting repeatable (LAR) octreotide. This new formulation requires only one monthly intramuscolar injection, and shows better acceptability and patient compliance to therapy. Data available to date show superimposable results of both standard octreotide and LAR octreotide in controlling symptoms, lowering hormone and tumor marker levels, and in reducing tumor growth. The availability of long-acting molecules have permitted the exploration of high-dose therapy in increasing tumor shrinkage and prolonging survival. Although there is a clear dose-response trend, the published data are not conclusive and further investigations are needed. The possible lack of cross-resistance between LAR octreotide and a different analog, Lanreotide, is a very stimulating finding and this might lead to the development of new therapeutical strategies in the management of neuroendocrine tumors.