Tuesday, July 22, 2008

MRD Negative

OK so we are back from our meeting with Dr. Thomas. I'm glad to say that we have some good news, that points to a good outlook on us being able to move forward. First a little back ground about bone marrow biopsies.

Each time Ann has a BMB done the marrow extracted is subjected to several tests. The first and "crudest" test is a direct examination of the cells in the marrow by a pathologist. This is called a smear, and it is in effect a simple count and categorization of the cells present under a microscope. I call it crude because it is impossible for a human to count or examine every cell taken in the sample.

Next is polymerase chain reaction (PCR) which seeks to amplify a single small piece of DNA from a large sample to the point that it can be easily spotted. In Ann's case a PCR test is trying to amplify the genetic signature that defines the leukemia. This is test has a better resolution than can be achieved by the human eye, but obviously can't be completed as quickly as looking at a slide on a microscope.

Finally there is fluorescent in situ hybridization (FISH) sometimes referred to as "fishing" by the medical staff. FISH takes fluorescent markers that are made from fragments of diseased DNA and then combined with fluorescent molecules, into a fluorescent probe. The BMB sample is dyed and combined with the fluorescent probe. If any of the cells in the sample are positive for the DNA being probed for they will turn up as glowing spots. The resolution of FISH falls somewhere between human eye examination and PCR, but it still takes a couple of days to prepare and finish.

Collectively theses tests are used to define the level of Minimal Residual Disease (MRD). Which means that over the 10,000 - 50,000 cells sampled collectively through the course of the tests performed, that they detect some number of leukemia cells. Its a ratio of disease present to health cells, which is why sometimes you see MRD expressed as a percentage (0.001% or 1% for example).

So we got the PCR and FISH tests back on Ann's BMB from last week and the results are 0% MRD or MRD Negative. Which means that the leukemia was susceptible to the chemo and we are headed to a probable remission on Thursday. I say "probable" because it will still have to be confirmed by a BMB Thursday. But this is a positive development and even our normally stoic leukemia doctor was smiling about it.

Thursday is gonna be a long, very stressful day.


Susan Carrier said...

Thanks for sharing this fabulous news so quickly.

Van said...

That is great news indeed :)

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