Sequential occurrence of BCR::ABL1-negative MPN and CML and vice versa: results from a real world cohort.

Chronic myeloid leukemia (CML) and BCR::ABL1-negative MPN were thought to be mutually exclusive, but synchronous and sequential cases have been reported. We screened 35,001 patients for BCR::ABL1 fusion or JAK2, CALR, or MPL mutations to investigate the sequential development of CML and BCR::ABL1 negative-MPNs. We discovered that 5.6% had primary CML followed by BCR::ABL1-negative MPN, and 5.8% had the reverse sequence. Notably, we identified higher JAK2 variant allele frequencies (VAFs) in patients developing secondary CML. Previous MPN did not compromise the effectiveness of tyrosine kinase inhibitors (TKI) in treating secondary CML. The emergence of secondary MPN appeared to be unrelated to JAK2 VAF progression or BCR::ABL1 transcript levels. Our research indicates that newly detected leukocytosis or thrombocytosis should prompt consideration of secondary MPN. It also showed that secondary CML had no negative impact on response to therapy when patients were treated according to CML guidelines.