Nonpositive Terminal Deoxynucleotidyl Transferase in Pediatric Precursor B-Lymphoblastic Leukemia

Terminal deoxynucleotidyl transferase (TdT) is a unique intranuclear DNA polymerase that catalyzes the template-independent addition of deoxynucleotides to the 3'-hydroxyl terminus of oligonucleotide primers. The expression of TdT is restricted to lymphoid precursors. It is a useful marker in distinguishing acute lymphoblastic leukemia (ALL) from mature lymphoid neoplasms. Although TdT- T-cell ALL has been reported in the literature rarely, the frequency and significance of TdT-nonpositive (TdT np ) B-cell ALL have not been examined extensively. We reviewed the immunophenotypes of 186 new cases of pediatric B-cell ALL and found 5 TdT np cases (2.7%). They showed significantly higher frequencies of a WBC count of more than 50,000/μL (>50.0 x 10 9 /L), CD10-, CD34-, and MLL gene rearrangement compared with those in TdT+ cases (3/5 [60%] vs 27/181 [14.9%], P =.03; 3/5 [60%] vs 11/181 [6.1%], P =.003; 4/5 [80%] vs 24/179 [13.4%], P =.002; 3/5 [60%] vs 9/181 [5.0%], P =.0019; respectively). These results indicate that nonpositive TdT does not rule out a diagnosis of ALL and suggest that TdP np B-cell ALL might be associated with CD10- and CD34- disease, a high WBC count, and MLL gene rearrangement.