The objectives of this study are:
* To assess the efficacy of lanreotide given every 4 weeks in participants with advanced or metastatic paraganglioma/ pheochromocytoma.
* To assess the toxicity and safety of lanreotide in participants with advanced or metastatic paraganglioma/ pheochromocytoma.
* To document the effects of lanreotide on markers of biochemical activity in participants with advanced or metastatic paraganglioma/ pheochromocytoma.
Primary endpoints:
• Assess efficacy by estimating the tumor growth rate while a patient is enrolled on study and comparing the growth rates on lanreotide to the pre-enrolment growth rate.
Secondary endpoints include measurement of:
* Overall survival (OS)
* Progression-free survival (PFS)
* Overall response rate (ORR) according to RECIST defined as partial response (PR) + complete response (CR)
* Magnitude of reduction in levels of 24-hour urinary metanephrines, catecholamines and magnitude of reduction in serum chromogranin A, evaluated every two months while enrolled on study.