It doesn't get much simpler than this: your body is very resilient. If you can get your bone marrow to actually stop producing the immature, leukemic blood cells, it will (fingers crossed) be able to recover, firing up the production lines again. A hard reboot, if you will. Slam it shut, any way you can, and in strange and mysterious ways, it will resume normal production sometime later.
The tricky part, then, is "turning off" the bone marrow. This is where chemotherapy comes in. Chemical therapy. Basically, pump a controlled amount of extremely high-dose chemicals into your body so that it can knock your marrow senseless. Kick the complete and utter crap out of it. Pummel it. Pound it relentlessly and trust that your body is strong enough to get back up off the mat when all is said and done.
Think you're tough now, Leukemia? Why don't you try a little daunorubicin on for size?
What's that, tough guy? You want a piece of me?
Let's see how tough you are after we throw in some Ara-C for good measure.
Too much chemotherapy and you're down for the count. Too little and you've got to get back in the ring again, already more than a little punchy from the first round. The chemo needs to be carefully measured and monitored. You cross your fingers, hoping that it comes back. With a dwindling supply of healthy blood cells, and no way, post-chemo, of producing any kind of blood cells, healthy or otherwise, you just hope that it comes back soon.
The alternatives? Well, we won't go there, because there really aren't any.