Is Bone Marrow Transplantation Risky With History Of Bypass Surgery?

My husband has just been diagnosed with sideroblastic anaemia. The consultant wants him to undergo bond marrow transplant within 6 m to 2 years depending on blood results. His bloods are stabl and he has never has a transfusion, he is 53 with a previous history of bypass surgery, never smoked. From my reading is this appraoch too risky