International reporting scale of BCR-ABL1 fusion transcript in chronic myeloid leukemia: first report from India

Achieving a major molecular response (MMR) is an important predictor of progression-free survival in chronic myeloid leukemia patients treated with imatinib. This requires accurate measurement of BCR-ABL1 transcripts normalized to a control gene, as well as defining a level (BCR-ABL1/control gene ratio) that will correlate with sustained clinical response. To make these measurements comparable between laboratories, an international scale (IS) is necessary. A BCR-ABL1/control gene ratio of 0.10% represents MMR in the IS. In collaboration with an international reference laboratory in Adelaide, S.A., Australia, we have established and validated a lab-specific conversion factor for expressing BCR-ABL1 transcript levels in the IS. In this report, we explain the process and steps involved in obtaining a valid lab-specific conversion factor for expressing BCR-ABL1 transcript levels in the IS.