What is PCR?

First of all PCR = Polymerase Chain Reaction. RT = Real Time and QT – Quantitative

Today most CML Specialists will opt for a QT-RT PCR, Quantitative, Real time, PCR. Quantitative means that there will be a measurable number returned as a result, versus qualitative PCR which just returns a “positive/Negative” answer.

Before going further you need to review the section on basic cell biology so that you will understand how PCR works.

PCR allows DNA or RNA as in the case of CML, to be amplified/replicated exponentially. More specifically, PCR looks for the fusion gene BCR/ABL ( Breakpoint Cluster Region on chromosome 22 region q11) Fuses with part of the ABL (ABL stands for Abelson, the name of a leukemia virus that carries a similar protein). Since ABL carries a domain that can add phosphate groups to tyrosine residues, the BCR ABL is also a tyrosine Kinase.

The BCR ABL gene is the oncogene responsible for activating a number of cell cycle controlling proteins and enzymes speeding up cell division and most importantly inhibiting DNA repair. PCR can be done on peripheral blood, blood taken from a vein in your arm, or aspirate from the bone marrow biopsy.

The general consensus is that PCR on peripheral blood and bone marrow aspirate return the same results, therefore it is perfectly acceptable for your quarterly PCR to be done on peripheral blood. PCR is a very sensitive test and there is currently a project in North America to standardize this test. This will ensure that in the future if a patient blood sample was sent to two different labs; both labs would return the same result. The ability to standardize this test is important for the long term capturing of minimal residual disease in CML.

Essentially 10 cc’s of your blood is given to the lab where your mRNA is isolated. PCR is a test that uses a couple of types of “primers” mixed in a pipette with your DNA and put into a thermal cycler. The thermal cycler heats and cools the DNA causing it to denature and therefore replicate. The primers used specifically target the fused BCR ABL gene and is a good way of looking directly at this gene.

As mentioned, this test is very sensitive and can look at 100,000’s of cells and with nested PCR close to 1 million cells can be checked.