The implication of FLT3 amplification for FLT targeted therapeutics in solid tumors

We investigated the patients with solid cancers harboring Fms-like tyrosine kinase 3 (FLT3) amplification using targeted sequencing of tumor tissue specimen and FISH assay. Simultaneously, FLT3-amplified patient-derived cells (PDCs) were generated to evaluate the sensitivity to FLT3 inhibition. A patient with metastatic colon cancer who was previously treated with more than 3(rd) line cytotoxic chemotherapy was found to have FLT3 amplification and then received regorafenib showing partial response. In two PDC cell lines with FLT3 amplification, FLT3 mRNA expression was increased, however, the growth of tumor cells was not significantly inhibited by either regorafenib or sorafenib which is known to block the activity FLT3. Additional drug combinations with mTOR inhibitor did not affect the cell proliferation of PDC. FLT3 amplification in solid cancers is infrequently observed using targeted genomic profile, as yet, FLT3 amplification does not seem to be an actionable target or a proper biomarker for FLT3 inhibitor sensitivity.