Terminal deoxynucleotidyl transferase in acute myeloid leukaemia

Between January 1980 and May 1981, 1966 marrow or blood samples from leukaemia patients were tested for terminal deoxynucleotidyl transferase (TdT) using nuclear immunofluorescence. The cells were also tested with a panel of immunological markers including monoclonal antibodies. Of 869 TdT positive cases detected, 555 were diagnosed as ALL and 32 as blast crisis of CGL; 226 were provisionally diagnosed as 'acute leukaemia' and finally diagnosed as ALL partly on the basis of immunological data; 56 TdT+ cases were provisionally diagnosed as acute non-lymphocytic or myeloid leukaemia; 266 cases of AML and 177 cases of CGL in blast crisis were TdT negative. Eleven of the above 'AML' cases were anti-cALL+ as well as TdT+ and were re-diagnosed and treated successfully as cALL. The remaining 45 were anti-cALL negative and finally diagnosed and treated, at least initially, as AML. Eleven of these cases had only 5-10% TdT+ cells which could have been normal, non-myeloid cells. Twenty cases had 11-50% TdT+ cells and 14 cases had 50-100% TdT+ cells. Of these latter two groups, details on 28 patients were available for evaluation. Three cases on review had no definitive myeloid cytochemistry and were haematologically AUL with a null-ALL phenotype (TdT+ DR+ cALL-). In 14 cases there was a large overlap (greater than 75%) of the proportion of cells with myeloid cytochemistry (Sudan black, peroxidase or esterases) and TdT; individual blast cells were therefore expressing these markers concurrently. In the remaining cases, mixtures of TdT negative myeloid and TdT+ (lymphoid?) cells may have coexisted although this was not proven unequivocally. Twenty-two cases of newly diagnosed TdT+ 'AML' received induction chemotherapy for AML (DAT regime) and only six (37%) obtained a complete remission. It is concluded that TdT positive 'myeloid' leukaemias do occur, albeit infrequently (approx. 5%) and may have a relatively poor prognosis.