ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive: Our clinical observations that rare CML patients with long-term (up to 20 years) failure of TKI treatment and a significant residual leukemic population (30-70% of BCR::ABL1 positivity in real-time PCR) did not experience hematologic progression or develop additional cytogenetic changes or ABL kinase mutations over long periods is surprising.