Molecular Response (MR) milestones for CML patients are determined based on the reduction in BCR::ABL1 mRNA and are defined as Major Molecular Response (MMR/MR3; BCR::ABL1 ≤ 0.1% International Scale (IS), MR4 (BCR::ABL1 ≤ 0.01% IS), and MR4.5 (BCR::ABL1 ≤ 0.0032% IS). The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.