detection of mycn dna in the cerebrospinal fluid for diagnosing isolated central nervous system relapse in neuroblastoma we present the case of a 1yearold female with stage4 neuroblastoma with mycn amplification she was treated with five chemotherapy courses resulting in normalization of elevated serum levels of tumor markers complete remission was achieved after allogeneic hematopoietic stemcell transplantation with reducedintensity conditioning nine months later however the tumor relapsed in the central nervous system cns the serum and cerebrospinal fluid csf levels of the tumor markers were normal but the mycn copy number was high only in the csf dna suggesting an isolated cns recurrence the mycn copy number in the csf dna was reflective of response to treatment