Clinical Phenotype and Response to Imatinib of Chronic Myelogenous Leukemia Patients Harbouring Atypical BCR-ABL Transcripts. A Retrospective Analysis From the French Group of CML (Fi-LMC) and the French Group of Molecular Biologists for Hematological Malignancies (GBMHM).
Authors: Deau Benedicte , Montveneur Mathias , Coiteux Valérie , Renneville Aline , Rigal-Huguet Francoise , Delabesse Eric , Tulliez Michel , Bories Dominique , Charbonnier Aude , Mozziconacci Marie-Joelle , Legay Thibault , Lippert Eric , Mahon Francois-Xavier , Rea Delphine , Cayuela Jean-Michel , Amé Shanti , Gaub Marie-Pierre , Gardembas Martine , Blanchet Odile , Audhuy Bruno , Buzyn Agnès , Intyre Elisabeth Mac , Andreoli Anna-Lisa , Reman Oumedaly , Contentin Nathalie , Bastard Christian , Ianotto Jean-Christophe , Ugo Valérie , Kiladjian Jean-Jacques , Brahimi Said , Dubruille Viviane , Brantus Jean-Francois , Sobh Mohamad , Morisset Stephane , Preudhomme Claude , Hayette Sandrine , Nicolini Franck E 
Published: October 2019

Abstract
Abstract 3378
Chronic Myelogenous Leukemia (CML) originates in the Philadelphia chromosome, a reciprocal translocation creating the fusion oncogene BCR-ABL. In 1–2% of CML cases, breakpoints fall outside the M-BCR gene on chromosome 22, leading to the synthesis of a variety of atypical BCR-ABL transcripts [shortened: e1a2 (m-BCR), e6a2, e8a2, b2a3 (e13a3), b3a3 (e14a3), or elongated transcripts: e19a2 (m-BCR)] and to the synthesis of different molecular weight BCR-ABL proteins that might have different tyrosine kinase activities. Thus, clinical phenotypes and BCR-ABL inhibition by tyrosine kinase inhibitors might be different and lead to different prognostic features. We retrospectively analysed at the national level, the clinical characteristics and the responses to imatinib (IM) of 63 patients with CML harbouring atypical BCR-ABL transcripts: 22 e1a2 [Group 1 (G1)], 20 e19a2 [Group 2 (G2)], 5 e8a2 [Group 3 (G3)], 4 e6a2 [Group 4 (G4)], 5 b2a3 [Group 5 (G5)], and 3 b3a3 [Group 6 (G6)] BCR-ABL transcripts. The general characteristics of the patients and their best response to IM are depicted in Table 1:
Table 1 Group 1(e1a2) Group 2 (e19a2) Group 3 (e8a2) Group 4 (e6a2) Group 5 (b2a3) Group 6 (b3a3) n 22 20 5 8 5 3 M/F 7/15 6/14 4/1 4/4 5/0 0/3 Median age (years) 70 69 43 57 62 47 CP/AccP/MBC 20/0/2 17/1/2 5/0/0 4/1/3 4/1/0 2/1/0 Sokal (L/H/I/Ukn)* 6/8/2/4 1/3/9/4 3/1/0/1 1/2/1/0 1/2/0/1 0/2/0/0 Leukocytes (G/l, median) 60.85 28.3 55 28.4 93 82.4 Hemoglobin (g/dl, median) 12 10.2 11.7 10.95 11.1 10.2 Platelets (G/l, median) 303 848 253 259 167 363 Monocytes (G/l median) 4.8 0.8 2.34 0.05 1.08 0.825 Additional Clonal Abnormalities at diag (% of patients) 20 28 0 29 25 0 IM duration (median, years) 1.55 1.38 1.58 0.8 1.13 1.42 Interval Diagnosis-IM (median, years) 1.31 1.48 1 1.17 0.87 1.66 Best response to IM* No response 20 0 0 0 0 0 CHR (%) 13 32 0 0 0 0 Minor CyR (%) 47 0 0 0 0 0 PCyR (%) 0 10 20 10 25 67 CCyR (%) 13 32 60 50 0 0 MMR (%) 7 26 20 40 75 33 Follow-up since diag (median, years) 3.24 1.57 1.6 3.82 1.5 1.68 (CP states for Chronic phase, AccP for accelerated phase, MBC for myeloid blast crisis, L for Low, I for intermediate, H for High, Ukn for Unknown, * For CP patients only)
Surprisingly, e1a2 and e19a2 transcripts seem significantly more frequent in females than in males conversely to typical BCR-ABL transcripts (p=0.01) and occurring more often in the elderly (p=0.05). The majority of the patients presented with typical cytological CML features, however, a significant monocytosis was observed in e1a2 and e8a2 atypical transcripts (p=0.0002). The median time on IM and the interval between diagnosis and IM were not statistically different between the 6 groups. Overall, there was no significant difference in the (hematologic, cytogenetic, molecular) responses to IM, but e1a2 transcripts seem less sensitive to this agent. The overall survival since diagnosis or since IM initiation was not different between atypical transcripts (p=0.55 and p=0.73 respectively), however, the progression-free survival (PFS) since diagnosis with e1a2 transcripts was significantly worse than for all other atypical transcripts (p=0.02) as shown in Figure 1:

The PFS since IM initiation was somewhat worse for e1a2 transcripts, but close to significance (p=0.09), but the follow-up is not very long yet. Fifteen patients among 63 had second generation TKIs (TKI2), 7 in group 1, 3 in group 2, 1 in groups 3, 4, 5, and 2 in group 6. Only one patient (b3a3 transcript) developed a MBC being on IM. Two patients developed a T315I BCR-ABL mutation (1 e1a2, and 1 e6a2). Two patients got allo-transplanted (1 e1a2 alive and well at last follow-up, 1 e19 a2 died from GVHD).
In conclusion, atypical BCR-ABL transcripts induce a particular molecular and subsequent clinical phenotypes, particularly e1a2 transcripts showing in this study poor prognosis features. The response of atypical BCR-ABL transcripts to IM might vary from that what it is for classical M-BCR transcripts, but a longer follow-up is needed.

Disclosures:
No relevant conflicts of interest to declare.