MRD

Tests for MRD using the polymerase chain reaction (PCR) can identify malignant cells based on their characteristic chromosome rearrangements. For example, PCR can detect evidence of the Philadelphia (Ph) chromosome which is found in about 95% of patients with chronic myelogenous leukemia (CML), 2%-10% of children with acute lymphoblastic leukemia (ALL), and 20%-50% of adults with ALL. The Ph arises through a reciprocal translocation between chromosomes 9 and 22 which creates a chimeric (hybrid) gene called bcr-abl that causes the malignancy. By PCR, the chimeric bcr-abl messenger RNA transcript can be detected. With PCR it is possible to detect one Ph-positive cell within a million normal cells.