There are a few way to classify transplants:
- autologous vs. syngeneic vs. allogeneic - are you your own donor, is the donor your identical twin, or is the donor someone else?
- related vs. unrelated - is the donor a family member?
- bone marrow vs. peripheral blood stem cells vs. umbilical cord stem cells - where did the donated cells come from?
- full conditioning vs. reduced intensity conditioning - do you get a full dose of chemotherapy or less than a full dose in preparation for the transplant?
You are asking about the last of these. It is called a "reduced intensity transplant" or a "non-myeloablative transplant" or simply a "mini-transplant". Unless you have a matched sibling your doctor is referring to an allogeneic unrelated reduced-intensity transplant. Although "BMT" implies a bone marrow transplant, we sometimes get lazy and say BMT when we mean "either a bone marrow or stem cell transplant".
With a mini-transplant, you get lower, less toxic doses of chemotherapy and/or radiation. Not all of your faulty bone marrow is eliminated but the donor's immune system (which becomes your immune system) can take on the job to fight the remaining disease cells.
Since the conditioning is less harsh, more people can tolerate it, making it possible to give transplants to a wider population of patients, particularly those of higher ages if they don't have other health issues that rule it out.
The pros and cons of mini-transplants compared with full transplants (or other treatments) are based on statistics about survival, transplant rejection, remission, relapse, and graft-versus-host disease (GVHD). Although the conventional wisdom may be that mini-transplants are less dangerous but carry a higher risk of graft rejection, all of these factors are being studied and doctors and patients are getting more and more information about the tradeoffs for various patient populations.
Much depends on the circumstances of each individual patient. Please let us know what your doctor says about the possibility of a mini-transplant for you.