Introduction

With current treatment, event-free survival rates in acute lymphoblastic leukemia (ALL) are about 75%. Therefore, relapse of ALL is still frequent with an incidence range close to that of neuroblastoma. Problems in the management of ALL relapse are the resistance of the leukemic cells and the reduced tolerance of patients to a second round of treatment after having already received intensive frontline therapy, resulting in a lower remission rate as well as a higher incidence of subsequent relapse and an inferior outcome overall.

Intensified polychemotherapy is essential for induction of a second complete remission (CR). Depending on a variety of prognostic factors, remission may be maintained with chemotherapy and cranial irradiation alone or with intensification of treatment by stem cell transplantation.

Diagnosis of relapse

The diagnosis of ALL relapse (i.e. the reappearance of leukemic cells in any anatomic compartment following CR) must be unequivocal. The work-up includes a careful physical examination as well as investigations of the bone marrow (BM), the cerebrospinal fluid (CSF) and, if necessary, biopsies of other involved sites (e.g. the testicles, lymph nodes or any other organs or tissues). As at initial diagnosis, the leukemic cells have to be characterized morphologically and by immunophenotyping, as well as by cytogenetic and molecular genetic procedures. Only this comprehensive information, together with clinical findings, allows one to classify the leukemic subtype adequately and to assess the prognosis of individual patients.