They start out in your bone marrow and they fill that up. But then they go other places, too. They can go to your lymph nodes or to your spleen or liver. Actually, they can go anywhere blood goes - and that's everywhere. Just as if the rabbits were not only in your house, but in every building in your city.
Blasts also cause trouble by forgetting to grow up.
They stay immature and keep dividing when they shouldn't . Because they are so immature, they can't do their work. Basically, blasts crowd out the good cells. Since they crowd out the red blood cells, a person with ALL is anemic, without enough red blood cells to carry the necessary oxygen or energy to the body. That's why fatigue is a sign of leukemia.