At 25 I had a 1 in 3 chance that I would get cancer. After I was in remission I had a 50% chance of relapse. With a transplant, my chance of relapse dropped to 20% - as long as I found a donor.
So, what were the odds that my sister would be a 100% match?
How did they even find out how she was a match? Well, through lot of confusing science involving an acronym "HLA".
HLA, or Human Leukocyte Antigens, are proteins located on white blood cells and on tissues in the body. Two people with matching HLAs means their tissues are immunologically compatible with each other. This HLA typing is the same process they use to match kidneys and other organs with siblings, relatives and other possible donors.
Remember your high school biology class when you talked about genes and how a spotted cat has a stripped brother? Yeah, me either.
It's all about what you inherit from your mom and dad. In the diagram, each person has two colored circles, each circle represents HLA groupings you inherit from your parents.
As a general rule, you have a 25% chance that one of your siblings is an identical HLA match. The further you go leave your genetic branch on the family tree, the less chance you have of finding a match. For instance, the chance of an HLA match with one of your parents or children is 12.5% and decreases on from there.
(Click here to check out more about HLA matching. It was created for matching kidney donors, but is a good guide to understanding HLA.)
So, the more siblings you have the higher chance you have of having a match, right? Yes and no. I have one sibling, and she was a 10/10 HLA match. Yet I met one woman who had nine siblings and none of her siblings were a match.
When matching donors, doctors look for certain HLA markers. Check out Be the Match for a great diagram about HLA markers. Some places look at 8 markers, some look at 10 - hence the 10/10 or 8/8 ratio.
The odds that my sister would be a match was 25%. The odds that she would be a 10/10 match was even slimmer. Who would have thought the kid who pushed me down the stairs during a little innocent roughhousing would go on to save my life?
And those were my odds of survival during chemo, a transplant, and the rest of my life. My most recent bone marrow biopsy results showed that I am now genetically 98% my sister, leaving me with a 2% chance of relapse. That's pretty good considering the odds from the beginning.
Stay tuned for when I show how a chimera like myself can get away with murder.