Pheochromocytoma Randomised Study Comparing Adrenoreceptor Inhibiting Agents for Preoperative Treatment

1. INTRODUCTION AND RATIONALE Pheochromocytoma (PCC) is a rare but clinically important catecholamine secreting neuro-endocrine tumour that typically arises from the adrenal gland. In addition, this neuro-endocrine tumour can also originate from chromaffin cells in sympathetic ganglia(1)(2). In this protocol, PCC refers to both adrenal and extra-adrenal chromaffin tumours with hypersecretion of catecholamines (i.e. norepinephrine and/or epinephrine). The annual incidence rate in the US population has been estimated to be 1-2 cases per 100,000 adult individuals (3). Data on the incidence and prevalence of PCC in the Netherlands have not been published. Based on the Dutch registry of pathology diagnoses (PALGA), we found an incidence of 117 cases of PCC in the year 2007 (unpublished observation).

PCCs may occur as part of an autosomal dominant inherited tumor syndrome, caused by germline mutations in the RET proto-oncogene (Multiple Endocrine Neoplasia type 2 syndrome), VHL gene (von Hippel-Lindau disease), NF1 gene (Neurofibromatosis type 1), or in one of the genes encoding the subunits of mitochondrial complex II, also called succinate dehydrogenase (SDHB, SDHC, SDHD)(4). PCCs are termed 'sporadic' when the family history for PCC is negative. Overall, about 25% of all PCC patients harbour a germline mutation. Notably, germline mutations in one of the PCC susceptibility genes may also be present in a significant number of patients with a sporadic PCC, with mutation rates varying between 7.5 - 14.6% in the populations studied(5-7). Therefore, genetic testing is recommended in all patients with PCC(7). Very recently, a new PCC susceptibility gene has been described, and it seems likely that future research will result in the discovery of other genetic mutations associated with PCC(8).

PCC constitutes a surgically curable cause of hypertension. Hypertension in patients with PCC can be either persistent or paroxysmal, but is absent in a minority of patients. It is a potentially life-threatening disease with a high risk for cardiovascular complications such as myocardial infarction, arrhythmias, cardiomyopathy, stroke and pulmonary edema(1). The clinical picture results from release of catecholamines by the tumour. This release can be evoked by stimuli that would normally not pose a hazard, such as surgery or general anaesthesia. Thus, preoperative treatment with alpha-adrenoceptor antagonists is usually recommended for prevention of these serious and potentially fatal complications(9). In one of the largest surgical series reported so far, perioperative mortality and morbidity were 2.4% and 23.6%, respectively(10).

According to the literature, about 10% of the patients with PCC are normotensive(1). A normal blood pressure at diagnosis is relatively frequent among carriers of one the aforementioned germline mutations, as these individuals are subjected to periodic biochemical screening for the presence of PCC. It has been demonstrated that intraoperative hemodynamic instability during adrenalectomy for PCC occurred to the same extent in MEN2a patients (most of whom were normotensive) as in patients without MEN2a (most of whom were hypertensive)(11). Thus, preoperative treatment with alpha -adrenoceptor antagonists is also recommended for normotensive patients with PCC (9,11), Historically, the noncompetitive and nonselective alpha -adrenoceptor antagonist phenoxybenzamine has been the drug of choice(12). Alternatively, doxazosin - a competitive and selective alpha 1-adrenoceptor antagonist - might be at least as effective asphenoxybenzamine with fewer side effects. Notably, it has been suggested that doxazosin results in a significant and clinically relevant reduction of postoperative hypotension(13). Severe postoperative hypotension necessitates admission to the intensive care unit (ICU), where volume resuscitation and norepinephrine are administered under strict monitoring of hemodynamics. Data on the optimal preoperative pharmacological management of patients with PCC are conflicting. For example, a recent study reported comparable effects of phenoxybenzamine and doxazosin on intraoperative hemodynamic control(14).This study, however, was retrospective in design and therefore affected by several confounding factors such as lack of randomisation, non-standardised intraoperative care, and use of historical controls. Until now, prospective randomised controlled trials comparing phenoxybenzamine and doxazosin have not been conducted. Thus, the preoperative drug therapy of choice remains an unresolved issue, and at a recent international PCC symposium it was concluded that no specific recommendations can be made on this subject(9). We performed a survey among all university medical centers in the Netherlands, showing that almost half of the centers prescribed phenoxybenzamine, whereas the other centers used doxazosine as the preoperative drug of choice for patients with PCC(15). Usually, these drugs are administered during 2-3 weeks before surgery. This preoperative medical preparation takes place either in the outpatient or inpatient clinic, depending on patient-related factors (e.g. disease severity, geographical considerations) and local experience.

Preoperative volume expansion is recommended in all patients with PCC(9). The rationale behind this recommendation is based on the notion that PCC is associated with a decreased intravascular volume, which is restored under influence of treatment with alpha -adrenoceptor antagonists. Without administration of volume expansion severe hypotension might ensue. Therefore, it is common practice to advise a liberal salt intake during alpha -adrenoceptor antagonist therapy and to administer a saline infusion (e.g. 2L NaCL 0.9% in 24 hours) shortly before surgery(9,15).