YES!! its risky as I mentioned there is a major risk of Graft versus Host Disease(GVHD) which is a life threatening condition and I have given a hint what is GVHD.
In newborns, bone marrow is present in all the bones but as soon as we reach our adulthood it is restricted to our long bones and flat bones; bones of legs, arms, feet, vertebrae, sternum, hip bone and few others.
For BMT, donor and recipient are matched by their Human leukocyte antigen(HLA) otherwise severe antigen antibody reaction can occur. There is likely a chance that a family member can donate marrow for you but its rare to get a match donor outside of family.
BMT transplant is needed for many other disorders apart from cancerous cases as I mentioned above like Thalassemia, Immune deficiency disorder and yeah the purpose of bone marrow transplant is to give patient new blood cells and immune system, cancerous cells are killed with the help of chemotherapy and radiation.
Thanks for sharing your views☺️, I tried not to use any professional term and wherever I have used it I have given little explanation about it.