Surface CD56 expression on leukemic cells in acute promyelocytic leukemia (APML) is considered an indicator of poorer outcome even in patients receiving conventional treatment.
In the present case, at initial diagnosis, the hallmark phenotype of APML was found (strong CD33 and cytoplasmic MPO expression, absence of HLA-DR expression).
Both CD34 and CD56 antigen expression was considered negative. The patient relapsed 3 years after reaching complete remission, and the hallmark surface antigen combination for APML was again found. In contrast, the leukemic cells now clearly coexpressed CD34 and CD56. Retrospective analysis revealed the presence of small CD34+ and CD56+ populations at initial diagnosis (<20%).
This case report suggests that the presence of a clone with minimal coexpression of CD34/CD56 in APML at initial diagnosis should not be neglected since it may be associated with earlier relapse.