Treatment of Isolated Extramedullary Relapse

With improved success in treating children with ALL, the incidence of isolated extramedullary relapse has decreased. The incidence of isolated CNS relapse is less than 5%, and testicular relapse is less than 1% to 2%.[213-215] As with bone marrow and mixed relapses, time from initial diagnosis to relapse is a key prognostic factor in isolated extramedullary relapses.[216] In addition, age older than 6 years at relapse was noted in one study as an adverse prognostic factor for patients with an isolated extramedullary relapse, while a second study suggested age 10 years as a better cutoff.[17,217] Of note, in most children with isolated extramedullary relapses, submicroscopic marrow disease can be demonstrated using sensitive molecular techniques,[218] and successful treatment strategies must effectively control both local and systemic disease. Patients with an isolated CNS relapse who show greater than 0.01% MRD in a morphologically normal marrow have a worse prognosis (5-year EFS rate, 30%) than do patients with either no MRD or MRD less than 0.01% (5-year EFS rate, 60%).[218]