Terminal deoxynucleotidyl transferase expression in acute myelogenous leukemia and myelodysplasia as determined by flow cytometry

The significance of terminal deoxynucleotidyl transferase (TdT) expression in acute myelogenous leukemia (AML) remains controversial. Therefore, we st udied TdT expression by flow cytometry in 120 previously untreated patients with AML or myelodysplatic syndrome (MDS) to determine the distribution of TdT-positive blasts and the intensity of TdT expression and to seek clinic ally significant associations. TdT expression measured by flow cytometry (f low TdT%) was heterogeneous, ranging from 0.1% to 87% (median, 8.5%), and 7 4 patients (62%) had at least 5% TdT-positive blasts. TdT positivity was as sociated with the M0 or M1 subtype and with expression of CD34 and CD7. No significant correlation was found between TdT expression and type of cytoge netic abnormality or rearrangement of immunoglobulin or T-cell receptor gen es. Remission lasted longer in patients with a flow TdT% < 5 than in patien ts with a flow TdT% > 5 (median, 95 weeks vs 55 weeks, p = 0.02); however, complete remission rates did not differ when patients were classified by in itial flow TdT%. Survival was slightly better for patients with flow TdT% l ess than 5% Among patients with a flow TdT% > 5%, those with a higher TdT i ntensity survived longer than those with a lower intensity. These data sugg est that quantitative TdT measurement may contribute to prognostic estimate in AML patients.