Could my brother have Leukemia?

I found out today my brother, who is 21 and i am 19 might have leukemia. He went to the doctor and they took blood and said it would take 3 weeks to come back. He did smoke, but recently quit, the horrible thing is that our aunt on our mothers side, had leukemia and it took her life. Im scared, and i want to know the likelyness that the leukemia is hereditary ( my aunt was also a smoker). I would also like to know if there is an increase in the chance i would have leukemia if my brother does end up having it. Also, about my brother, about 8-10 years ago he broke his arm, and after having people sign his cast he hated it and painted it with house paint that contained benzen ( not sure thats spelled right) and it burned all the skin right off his arm, and the doctor told us then that he would need to be routinely checked for cancer as benzen was know to contributing to the disease.. could his be the cause? Thank you for any help.. i just want to better understand the situation.