Treatment-influenced associations of PML-RARα mutations, FLT3 mutations, and additional chromosome abnormalities in relapsed acute promyelocytic leukemia

Mutations in the all-trans retinoic acid (ATRA)-targeted ligand binding domain of PML-RARα (PRα/LBD⁺) have been implicated in the passive selection of ATRA-resistant acute promyelocytic leukemia clones leading to disease relapse.Among 45 relapse patients from the ATRA/chemotherapy arm of intergroup protocol C9710, 18 patients harbored PRα/LBD⁺ (40%), 7 of whom (39%) relapsed Off-ATRA selection pressure, suggesting a possible active role of PRα/LBD⁺. Of 41 relapse patients coanalyzed, 15 (37%) had FMS-related tyrosine kinase 3 internal tandem duplication mutations (FLT3-ITD⁺), which were differentially associated with PRα/LBD⁺ depending on ATRA treatment status at relapse: positively, On-ATRA; negatively, Off-ATRA. Thirteen of 21 patients (62%) had additional chromosome abnormalities (ACAs); all coanalyzed PRα/LBD mutant patients who relapsed off-ATRA (n = 5) had associated ACA. After relapse Off-ATRA, ACA and FLT3-ITD⁺ were negatively associated and were oppositely associated with presenting white blood count and PML-RARα type: ACA, low, L-isoform; FLT3-ITD⁺, high, S-isoform. These exploratory results suggest that differing PRα/LBD⁺ activities may interact with FLT3-ITD⁺ or ACA, that FLT3-ITD⁺ and ACA are associated with different intrinsic disease progression pathways manifest at relapse Off-ATRA, and that these different pathways may be short-circuited by ATRA-selectable defects at relapse On-ATRA. ACA and certain PRα/LBD ⁺ were also associated with reduced postrelapse survival.