Clinical utility of terminal deoxynucleotidyl transferase and adenosine deaminase determinations in adult leukemia with a lymphoid phenotype.

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Abstract
A prospective study was done to assess the clinical utility of terminal deoxynucleotidyl transferase (TdT) and adenosine deaminase (ADA) assays in adult leukemia with a lymphoid phenotype. The study population consisted of 58 patients with adult lymphoblastic leukemia (ALL) at onset, 12 with lymphoblastic lymphoma, 15 with acute unclassifiable leukemia (AUL) and 30 with lymphoid or mixed acute phase of Philadelphia chromosome-positive (Ph'' +) chronic myelogenous leukemia (CML). TdT was present in all cases of T-ALL, in 90% of non-T, non-B ALL, and absent in B-ALL: the ADA activity was significantly higher (P < 0.01) in T-ALL. TdT was found in 75% of lymphoblastic lymphomas, in 78% of lymphoid and in 50% of mixed CML transformations; higher ADA activity correlated with TdT positivity in AUL and CML blastic transformations (P < 0.001). TdT-positive ALL had a better chance of response to therapy than TdT-negative ALL (P < 0.01), but survival was not statistically different. TdT was undetectable in the peripheral blood of patients with ALL in complete remission and within the normal range in bone marrow (0.1%-8% of nucleated cells); median ADA activity was as in control subjects. Relapsing ALL patients had TdT and ADA enzymatic activities as before therapy; TdT immunofluorescence test (IF) was positive in 69% of bone marrow and in 100% of CNS relapses. Twenty percent of TdT-positive ALL at onset became TdT-negative in bone marrow at relapse. TdT IF test was instrumental in detecting meningeal leukemia but neither TdT nor ADA could be used as indicators of complete remission or impending relapse because TdT-positive cells were present in normal marrows and wide fluctuations of TdT IF values and of ADA activity were observed in remission.