Does ATRA Confirm to Play a Role in the Better Relapse Free Survival of Infants with Acute Lymphoblastic Leukemia?

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Abstract Abstract 1515 Treatment achievements in infant's acute lymphoblastic leukemia (ALL) are still very modest. Despite of many attempts, the creation of novel, based on the molecular mechanisms, clinically approved and safe therapy strategies for this group of patients (pts) seems to be slow, so far. We also have developed a new treatment approach for infants with acute leukemia – MLL-Baby protocol, which includes 1 or 2 weeks ATRA consecutive courses at the dosing schedule of 25 mg/m2/d adjusted to age, started immediately after induction completion, alternating with standard chemotherapy and/or simultaneously applied with re-inductions. Rationale for ATRA application and MLL-Baby details were introduced in our previous report (ASH 2007 Abstract #2828). We have described there a small group of 19 primary diagnosed ALL infants, who underwent MLL-Baby protocol treatment in comparison to the group treated by standard chemotherapy with 20 months (mo.) median of follow up. ATRA-containing regimen has been shown well tolerated and improved early relapse free survival (RFS) significantly. Aim. To re-assess the ATRA efficacy in more representative group of pts with longer time of follow up. From September 2003 108 pts with primary ALL younger 12 mo. were non-randomly allocated either to ATRA (+) treatment approach (MLL-Baby) – 75 pts or ATRA (-) standard chemotherapy (mainly ALL-MB) – 33 pts due to decision of the treating physicians from 24 participating clinics in Russia and Belarus. Parents' informed consent was signed in all cases. The trial was approved by Ethics Committees. Both ATRA (−) and ATRA (+) groups were similar by the initial characteristics: median age 6 (1–11) and 6 (0–11) mo.; m/f ratio 12/21 and 25/50; initial WBC 96,7 (0,7–940) and 83,9 (1,6–2058) per microliter respectively, although CNS involvement seems to be more frequent in ATRA (+) group: 4 (12%) and 18 (24%) pts correspondingly. MLL rearrangements (MLL pos.) were found in 15 (53,6%) from 28 examined ATRA (−) pts and in 53 (70,7%) from 75 ATRA (+) pts. BI phenotype predominance was evident in ATRA (+) group - 39 (52,7%) out of 74 examined pts. The number of pts who have achieved CR was equally high in both schedules: 28 (84,9%) and 67 (89,3%) but the relapses rates remains significantly different: 16 (57,1%) and 16 (23,8%) pts in ATRA (-) and ATRA (+) groups respectively (p=0,001). Eight years RFS is 0,36 ± 0,08 and 0,59 ± 0,06 (p=0,02); cumulative incidence of relapses (RCI) is 0,62 ± 0,01 and 0,31 ± 0,004 (p=0,03) in ATRA (−) and ATRA (+) groups correspondingly, although EFS: 0,54 ± 0,06 vs. 0,33 ± 0,08 (p=0,17) and OS: 0,59 ± 0,06 vs. 0,36 ± 0,08 (p=0,09), median of follow up - 36 mo. (2 - 105), did not differ significantly between 2 groups ATRA (+) and ATRA (−) respectively due to the high proportion of induction and remission deaths. Among 75 pts treated by MLL-Baby – 7 (9,3%) died in induction and 7 (10,4%) out of 67 pts who achieved CR died in remission with median time to death – 2 mo., mostly because of severe infections. Out of 46 MLL pos. pts from ATRA (+) group who achieved CR, 14 (30%) pts relapsed, RFS is 0,59 ± 0,08 and RCI 0,40 ± 0,007. In contrast, in ATRA (−) group the relapse incidence in MLL pos. pts was very high - 12 (80%) out of 15 pts who achieved CR (p=0,008), RFS is 0,20 ± 0,10 (p=0,01) and RCI 0,80 ± 0,01 (p=0,02) correspondingly. In univariate analysis the following risk-factors: age < 6 mo. (p=0,001); MLL rearrangements (p=0,004) and dexamethasone response on Day 8 (p=0,01) have a significant negative impact on EFS in group of pts treated by MLL-Baby. Cox-regression analysis confirms the negative value of the same risk-factors: MLL pos. status with Hazard Ratio (HR) 3,8 (95% CI 1,32-10,9) p=0,01; age HR 3,18 (95%CI 1,5–6,8) p=0,003 and Day 8 response HR 3,16 (95% CI 1,4–7,1) p=0,005. Conclusions. The updated results in our cohort of 75 patients demonstrated that ATRA confirms effectiveness in the relapses prevention in infants suffering from ALL, if used in combination with standard chemotherapy without any escalation and bone marrow transplantation. Although the molecular mechanisms of ATRA effect are still poorly understood and need to be deeply explored, it might be recommended for randomization within representative international studies, particularly to the MLL rearranged infant's ALL. Great efforts in non-relapse mortality reduction should be applied by all participating clinics. Disclosures: No relevant conflicts of interest to declare.

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