There are many very serious risks and side effects to a bone marrow transplant. These include:
Severe and continuous bleeding
Infertility or sterility
Numbness in your arms and legs
Secondary cancers. The transplant procedure increases the risk of developing another cancer.
Death. In a very small percent of patients, the complications may lead to overwhelming infections or organ failure despite aggressive attempts to prevent death.
Another possible problem is that cells from a donor might not match your cells well enough and the new cells can begin attacking your cells. This is called graft versus host disease and is a type of "rejection." This can be a serious problem, but it also can help to cure the cancer because the new cells also will attack any cancer cells that are left.
In fact, in some protocols under investigation, donor bone marrow cells are transplanted into recipients who have not had their own bone marrow eliminated. These so-called "mini-transplants" theoretically work well because of the graft-versus-tumor effect. These types of transplants are being investigated mainly for use in situations in which a full transplant may not be possible or where other options are limited.