ZBTB16-RARα-Positive Atypical Promyelocytic Leukemia: A Case Report.

Background: The majority of patients with acute promyelocytic leukemia (APL) manifest a specific chromosomal translocation t(15;17)(q22;q21), characterized by the fusion of RARA and PML genes. However, a proportion of APL cases are due to variant translocations, being t(11;17) (q23;q21) the most common amongst them. With the major exception of ZBTB16-RARA t(11;17) APL, these variant APL cases present similar morphological features as classic APL and are characterized by a lack of differentiation response to retinoids.

Case Summary: We describe the case of variant APL with the ZBTB16-RARA fusion gene, showing a distinct morphology of classical APL, characterized by crystalline intracytoplasmic inclusions in both peripheral blood (PB) and bone marrow (BM) patients' blasts. Our patient was treated with two courses of intensive chemotherapy, initiating maintenance treatment with all-trans retinoic acid (ATRA) on day twenty-eight of the second course. Our patient achieved complete remission (CR) once the intensive chemotherapy was combined with ATRA.

Conclusions: This is the second case described of APL with t(11;17) that showed crystalline intracytoplasmic inclusions. The finding of these morphological features may suggest the presence of a variant translocation with RARA, being that both cases described are related to the presence of t(11;17). Despite induction treatment with intensive chemotherapy that included a seven-day continuous treatment with cytarabine (200 mg/m), plus daily idarubicin (12 mg/m) during the first three days, our patient did not achieve complete remission (CR) until scheduled 3 + 7 regimen combined with ATRA treatment was established. This observation suggests that ATRA may be partially effective in some ZBTB16-RARA APLs.