[Detection of low numbers of malignant cells in patients with leukemia or non-Hodgkin lymphoma: use of immunological markers].

Several different techniques have been used for the detection of low numbers of malignant cells in patients with leukemia or non-Hodgkin lymphoma, e.g. cytomorphology, cytogenetics, recombinant DNA techniques and immunological marker analysis. The detection limit of most techniques, however, is not lower than 1% (i.e. 1 malignant cell in 100 normal cells). Most immunological markers represent differentiation antigens, which are also expressed by normal cells. Nevertheless, it is possible to use these differentiation antigens for the detection of low numbers of malignant cells, since the occurrence of positive cells outside their normal homing areas can be indicative of malignancy. A useful marker for the detection of low numbers of acute lymphoblastic leukemia (ALL) cells in the cerebrospinal fluid is terminal deoxynucleotidyl transferase (TdT). Although TdT positive cells normally occur in low frequencies in bone marrow and blood, the combined detection of TdT and a T cell marker at the single cell level, allows detection of very low numbers of T-ALL cells. The detection limit of this technique is at least 0.01%. Such a low detection limit allows the adjustment of remission and staging criteria as well as the individualization of therapy.