Oral VP16 combined with ATRA and realgar-indigo naturalis formula as complete oral induction regimen is an fast，safe and effective regimen during induction to reduce mortality in high-risk acute promyelocytic leukemia Free

Background： Early death in high-risk acute promyelocytic leukemia (APL) is closely related to the leukocytosis at the onset of the disease. During induction, cytoreductive chemotherapy is a critical early intervention. Current international and Chinese guidelines recommend all-trans-retinoic acid (ATRA) plus arsenic tri-oxide, combined with either an anthracycline or cytarabine. Realgar-Indigo naturalis formula (RIF)，an oral realgar (As4S4)-containing formula, has been incorporated into the Chinese APL guideline. However, the intravenous cytotoxic agents must be administered in specialized inpatient units. During the COVID-19 pandemic we treated two pts(pts) with newly diagnosed high-risk APL in the emergency department with an exploratory all-oral regimen consisting of etoposide (VP-16) plus ATRA and RIF. Both pts achieved complete remission and have remained disease-free for five years (Leuk Res Rep,2021). To evaluate the efficacy and safety of oral etoposide combined with ATRA and RIF in high-risk APL, we have initiated a single-arm, prospective cohort study (ChiCTR2100053926).

Method: Once high-risk APL was suspected, ATRA 25mg/m²/day, hydroxyurea (Hu) and oral VP16 100-150 mg/day were given simultaneously. Hu and VP16 discontinued when white blood cells (WBC) creases to ≤10×10⁹ /L. RIF was administered by 60mg/kg/day when PML::RARA fusion gene or t (15;17) translocation was confirmed. RIF was used no more than 45 days. Corticosteroid was added during induction to prevent differentiation syndrome. The primary end point was complete remission (CR) rate. Relapse, survival and safety were assessed.

Results: From January 2022 to February 2025, 35 pts were included. Median follow-up time was 17.1 (0.2-42.7) months. The median age was 37(18-65) years with 74.3% (26/35) males. The median counts of WBC, platelet, fibrinogen level and PML::RARA transcript level were 20.0 (10.2-145.5) ×10⁹/L, 25(5-83) ×10⁹/L, 122 (41-267) g/L and 33.5(18.9-88.8) %. In PML::RARA sub-types, S, L, and V type were 62.3% (22/35), 34.3% (12/35), 2.9% (1/35), and 31.4% (11/35) expression CD34 by multi-parameter flow cytometry. Mutated FLT3-ITD and FLT3-TKD were found in 40.0% (14/35) and 5.7% (2/35) pts respectively, and 59.1% (13/22) pts had mutated FLT3-ITD (p=0.006) in PML::RARA (S) type. Except for t (15;17), 20.0% (7/35) pts had additional abnormal karyotype.

As a result of 5.7% (2/35) pts dying of cerebral hemorrhage within 5 days, the response and survival were assessed in 33 pts. During induction, the median time of oral VP16 administration was 9 (5-13) days with a median dose of 1150 (650-1650) mg. Nine (27.3%) pts used venetoclax to combinate with VP 16 with a median dose of 100 (50-300) mg. All pts achieved CR after 45(28-63) days with a median PML::RARA transcript level of 0.0089 (0-5.6) %. 11 pts (33.3%) pts achieved complete molecular remission (CMR) after induction. After 2.4 (1.4-5.5) months, all pts achieved CMR. None of the 33 pts died during the induction. The median infusion of red blood cells, platelet and fibrinogen were 4 (0-18) U, 3.5(0-8) U, and 15 (0-61) g. Neutropenia was observed in 36.3% (12/33) pts with a duration of 5 (1-17) days. Only 1 patient occurred obvious differentiation syndrome. Ten (30.3%) pts experienced grade 1-2 hepatotoxicity and 3.0%(1/33) grade 3. In each case, 3 (9.1%) pts suffered from gastrointestinal bleeding and cerebral hemorrhage respectively，and 1 (3.0%) patient experienced diffuse alveolar hemorrhage.

After 6.9 (4.0-8.3) months, 3(9.1%) pts experienced molecular relapse, and 2 (6.1%) pts suffered from haematological relapse after 20.5 and 30.8 months. In the two haematological relapse pts, one patient acquired new mutated FLT3-TKD, and the other patient's mutated FLT3-ITD at diagnosis contributed to the relapse. The 2-year relapse free survival and overall survival were 80.0% (95%CI, 59.2-100%) and 91.7% (95%CI, 76.0-100%). Univariate and multivariate analysis showed no correlation between recurrence and S or L type, mutated FLT3-ITD, dose of VP16.

Conclusion: Compared with historical cases, oral VP16, instead of intravenous cytoreductive agent, in combination with ATRA and RIF as complete oral induction in high-risk APL, could control leukocytosis effectively and safely. Meanwhile high CR rate, RFS and OS could also achieve. In addition, this regimen is convenient for pts to receive fast and professional treatment as soon as possible without the limitation of space.