"pre-B"

I think there are probably some more medically precise explanations of this on the sites in the right margin (and elsewhere), but here is a dumbed-down explanation. I was going to make a bunch of disclaimers here, but our oncologist just read the post and confirmed that it is right. :)

There are several different types of blood cells, including "B" cells, "T" cells, and some others. Blood cells, including B cells, are made in the bone marrow. You start with the now-famous "stem" cells. There is maturing and cell division. You then get some intermediate cells which mature and divide. Then eventually you end up with functional B cells.

Ben's cancer exists in the intermediate cells between the stem cells and the mature cells. You have a bunch of non-functional "pre-B" cells dividing like crazy and squeezing the healthy cells out. So what we are doing is killing all of the cancerous "blast" cells. Once that is done, the healthy cells can grow and he'll be OK. It's kind of like pruning a dying tree or cleaning up an overgrown garden.

I will try to find some links to a better explanation and post them, but hopefully this helps a little.