In addition to having greater sensitivity than cytogenetic analysis—qRT-PCR can detect 1 CML cell in >= 100,000 normal cells—the strong correlation between results obtained in the bone marrow and peripheral blood permits evaluation of BCR-ABL mRNA in either type of sample (Branford et al., 1999). Here, ABL1 is linked to chronic myelogenous leukemia, BCR-ABL1 positive.