Detection of minimal residual disease: relevance for diagnosis and treatment of human malignancies.

Minimal residual disease (MRD) is the tumor burden that is present after a course of treatment that has resulted in clinical remission. For hematopoietic malignancies, techniques for detection of this minimal tumor burden are being used to monitor MRD. These involve methods that are capable of identifying very low numbers of neoplastic cells in an otherwise normal marrow or lymph node. Patients with demonstrable residual neoplastic cells tend to do worse than patients without detectable cells; however, results depend on the timing of the assay and whether the detectable neoplastic cells appear to be increasing in number with subsequent assays. For bone marrow transplantation, assays incorporating chimerism analyses, cytogenetics, and morphology are used to regulate therapy.