Evolution of a FLT3-TKD mutated subclone at meningeal relapse in acute promyelocytic leukemia (H021)

Here we report the case of an acute promyelocytic leukemia (APL) patient who, though negative for FLT3 mutations at diagnosis, developed isolated FLT3-TKD positive meningeal relapse, which, in retrospect, could be traced back to a minute bone marrow subclone present at first diagnosis. Initially, the 48-year old female diagnosed with high-risk APL had achieved complete molecular remission after standard treatment with all-trans retinoic acid (ATRA) and chemotherapy according to the AIDA protocol. 13 months after start of ATRA maintenance the patient suffered clinically overt meningeal relapse along with minute molecular traces of PML/RARA in the bone marrow. Following treatment with arsenic trioxide (ATO) and ATRA in combination with intrathecal cytarabine and methotrexate, the patient achieved a complete molecular remission in both cerebrospinal fluid (CSF) and bone marrow, which currently lasts for two years after completion of therapy. Whole exome sequencing and subsequent ultradeep targeted re-sequencing revealed a heterozygous FLT3-TKD mutation in CSF leukemic cells (p.D835Y, c.2503G>T, 1000/1961 reads (51%)), which was undetectable in the concurrent bone marrow sample. Interestingly, the FLT3-TKD mutated meningeal clone originated from a small bone marrow subclone present in a variant allele frequency of 0.4% (6/1553 reads) at initial diagnosis. This case highlights the concept of clonal evolution with a subclone harboring an additional mutation being selected as the “fittest” and leading to meningeal relapse. It also further supports earlier suggestions that FLT3 mutations may play a role for migration and clonal expansion in the CSF sanctuary site.H021

• Type: Other
• Archiver: European Genome-Phenome Archive (EGA)