Aberrant Myeloid Marker Expression in Precursor B‐Cell and T‐Cell Leukemias

The World Health Organization (WHO) characterization of the immunophenotype of precursor B‐cell acute lymphoblastic leukemia (BALL)/lymphoblastic lymphoma (LBL) includes the possible expression of myeloid cluster of differentiation (CD) markers CD13 and CD33. In precursor T‐cell ALL/LBL, myeloid markers CD13 and CD33 are frequent while CD117 is rare. In the present investigation, 58 cases of confirmed precursor B‐cell ALL/LBL were evaluated for the presence of CD13, CD33 and CD117. Of the 13 (22.4%) cases that positively expressed myeloid markers, 8 (62%) expressed CD13; 10 (77%) expressed CD33; and 1 (8%) expressed CD117. Four (31%) expressed both CD13 and CD33, and 1 (8%) expressed CD13, CD33, and CD117. 18 cases of confirmed precursor T‐cell ALL/LBL were analyzed for myeloid markers CD13, CD33, CD117 and MPO. Of the 5 (28%) expressing myeloid markers, 3 (60%) were positive for CD13; 3 (60%) for CD33; 3 (60%) for CD117; and 1 (20%) for MPO. One (20%) was positive for both CD13 and CD117; 1 (20%) for CD13, CD33 and CD117; and 1 (20%) for CD13, CD33 and MPO. These markers portend a poor prognosis compared to ALL/LBL cases without myeloid antigens, and a poor response to drug therapies targeting conventional ALL/LBL. Future studies will be directed to correlation of these markers with prognosis and therapeutic response, as well as whether drug therapies targeting myeloid antigens could be of use in treatment.