• Difference in recurrence rate at the end of treatment
  

• Difference in reduction in size of IRF (as assessed by CT/MRI)
  
• Difference in renal function
  

Idiopathic retroperitoneal fibrosis (IRF) is a rare condition hallmarked by the presence of a retroperitoneal mass consisting of chronic inflammatory infiltrate and abundant fibrous tissue. IRF usually presents as a systemic inflammatory disease, with constitutional symptoms (e.g. fatigue, weight loss) and high acute-phase reactants; in addition, IRF patients often complain of abdominal or lumbar pain and, if ureteral involvement is present, they may also show oliguria and symptoms related to uremia.

Ureteral obstructive disease is usually managed by placement of ureteral indwelling stents, nephrostomy tubes or, in the more severe cases, surgical ureterolysis. These approaches are usually followed by medical treatment.

The medical treatment of IRF is largely empirical: corticosteroids are routinely used, but a number of reports have shown that tamoxifen may also be effective. However, no prospective controlled trials have been conducted in patients with this condition. In this study, we compare the efficacy of prednisone and tamoxifen in IRF patients.

Patients who received a diagnosis of IRF will be enrolled, while patients with secondary forms of retroperitoneal fibrosis (e.g. drugs, infections, radiotherapy) will be excluded. When present, ureteral obstruction will be managed by ureteral stents/nephrostomy/ureterolysis. All patients will then receive oral prednisone (1 mg/kg/day) for one month, at the end of which they will be randomized to receive either tamoxifen (0.5 mg/kg/day at fixed dose for 8 months) or prednisone (0.5 mg/kg/day for the first month, 0.25 mg/kg/day for the second and third months, and then tapered off during the ensuing 5 months). A CT/MRI study will be performed before the start of treatment, four months after randomization and at the end of treatment. All patients will be followed up for at least 18 months after the end of treatment.

Disease remission will be defined on the basis of clinical symptoms related to IRF (e.g. pain, constitutional symptoms), levels of acute-phase reactants (erythrocyte sedimentation rate, C-reactive protein), and ureteral obstruction (as assessed by sonography or CT/MRI scan).