Since the abundance of BCR::ABL1 fusion gene correlates better with CML cell number as compared to BCR::ABL1 transcript levels, we apply a non-linear mixed effect model to analyze the ratio of these two observables to achieve a better understanding of how much BCR::ABL1 expression changes throughout treatment. This evidence concerns the gene ABL1 and chronic myelogenous leukemia, BCR-ABL1 positive.