Assessment of extramedullary leukemic infiltration in childhood acute lymphoblastic leukemia and its clinical use. Review and original data
Abstract
Minimal residual disease (MRD) has become a crucial criterion for the risk stratification within modern protocols for the treatment of both childhood and adult acute lymphoblastic leukemia (ALL). The most data obtained so far apply to the bone marrow and studies on extramedullary MRD are scarce.
According to the published data, levels of MRD in peripheral blood and bone marrow correlate well in T-ALL, whereas in B-cell precursor ALL the correlation is weak and MRD in blood is mostly more than one log lower than in the bone marrow. Despite this fact, MRD in peripheral blood during the induction therapy is predictive of prognosis, as shown by our results for day 15 of the ALL IC-BFM 2002 protocol.
There is still lack of information on the benefit of cerebrospinal fluid examination by PCR and flow cytometry at initial diagnosis in patients with ALL. Flow cytometry presumably reveals more positive results than "classical" microscopy.
Both PCR and flow cytometry are suitable for the examination of leukemic involvement at the time of CNS relapse, but their informative value during the treatment of relapse is questionable due to insufficient DNA quality for the purpose of PCR and due to fast sample degradation for the purpose of flow cytometry. An unambiguous benefit of PCR lies in the assessment of simultaneous bone marrow infiltration at diagnosis of isolated extramedullary relapse, which, if present, confers inferior prognosis.