Central Nervous System Relapse in Patients with Acute Promyelocytic Leukemia Treated with All-Trans Retinoic Acid and Reinforced Anthracycline Monochemotherapy.
Authors: Montesinos Pau , Gonzalez Jose D. , Vellenga Edo , Rayon Chelo , Parody Ricardo , Leon Angel , Esteve Jordi , Bergua Juan , Milone Gustavo , Sanz Miguel A. 
Published: October 2019

Abstract
Background: Central nervous system (CNS) relapse can complicate the course of patients with acute promyelocytic leukemia (APL) treated with all-trans retinoic acid (ATRA) and chemotherapy, especially of those with high WBC at diagnosis (≥10 × 109/L). While ATRA and anthracyclines do not crosses the cerebrospinal fluid barrier, some trials for APL includes the use of intratechal prophylaxis or high-dose cytarabine, at least in high-risk patients, to avoid the CNS relapses. However, the convenience of CNS prophylaxis in APL patients is a matter of controversy.
Objectives: Analyze the incidence and characteristics of CNS involvement at first relapse, in patients with newly diagnosed APL treated with ATRA and reinforced anthracycline monochemotherapy, without CNS prophylaxis.
Methods: From 1999 to 2005, 564 patients (median age 40 years, range 2-83) were included in the PETHEMA LPA99 trial. Induction therapy consisted of ATRA and idarubicin. Patients in CR received 3 monthly courses of risk-adapted consolidation therapy as follows:
“low-risk” patients (WBC <10×109/l and platelets >40×109/l), idarubicin 5 mg/m2/d × 4 (course #1), mitoxantrone 10 mg/m2/d × 5 (course #2), and idarubicin 12 mg/m2/d × 1 (course #3); “intermediate-risk “ (WBC <10×109/l and platelet <40×109/l) and “high-risk” (WBC >10×109/l) patients received ATRA (45 mg/m2/d × 15) in combination with reinforced chemotherapy (Idarubicin 7 mg/m2/d in the course #1 and two days instead of one in the course #3).
Maintenance therapy consisted of low-dose oral chemotherapy (mercaptopurine and methotrexate with ATRA). We measured the cumulative incidence (CI) of CNS involvement at first relapse during the course of APL patients who achieved the CR.
Results: CR was achieved in 511 patients (91%). The median follow-up of the cohort was 57 months (range 20–94 months). Overall, 52 patients relapsed, of whom 5 presented a first relapse in CNS. In all cases, CNS relapses occurred without bone marrow or other extramedullary involvement. CNS relapses occurred after a median of 14 months (range 10–41 months) from the achievement of CR. At the initial diagnosis, APL were classified, according to the Sanz score, as low-, intermediate- and high-risk, in 0, 2, and 3 patients, respectively. The median WBC at diagnosis was 34.5 × 109/L (range 1.9–68.8 × 109/L), and 4 patients showed a Bcr3 PML-RARalpha isoform. Using a competitive-risk method, the overall 5 year CI of CNS relapse was 1.03%. The 5 year CI of CNS relapse in low-, intermediate- and high-risk patients was 0%, 0.77% and 2.71%, respectively (low- vs high-risk and intermediate vs high-risk; p=0.12 and p=0.11, respectively). The 5 year CI of CNS relapse in patients with Bcr3 and Bcr1 PML-RARalpha isoform was 0.45% and 2.44%, respectively (p=0.12).
Conclusion: Despite the lack of intratechal prophylaxis or high-dose cytarabine in the therapeutic schedule of the LPA99 trial, the overall 5 year CI of CNS relapse was very low (1%). Our results does not hold up the systematic use of CNS prophylaxis in APL patients treated with ATRA and reinforced anthracycline monochemotherapy.