A clinical case analysis found that SPTBN1-type III receptor tyrosine kinase (FLT3) fusion was rare in atypical chronic myeloid leukemia (aCML), but abnormal FLT3 was sensitive to immunotherapy, and as a new type of constitutively active tyrosine kinase, it was also sensitive to tyrosine kinase inhibitor therapy 116. Here, FLT3 is linked to atypical chronic myeloid leukemia, BCR-ABL1 negative.