When we normally give cancer drugs to patients we work to what is known to be their primary toxicity. This means that we give the maximum amount of the drugs to try to kill the cancer cells, but not beyond the point where they may cause damage to normal body organs. If you go above this dose there is a point where the patient can become seriously ill. The reason why very high doses of drugs can not be given to all patients with cancer is that there clearly has to be a relationship between the amount of drug given to a patient and the amount of cancer cells that are killed. Non-Hodgkin's lymphoma a direct relationship between the amount of drugs given and the amount of tumor cells that are killed has been established.
More drugs just seem to increase the toxicity with no increased benefit.
If one decides that high dose chemotherapy is an option, then a way of rescuing the blood system has to be used. There are pluses and minuses to both autologous transplantation and allogeneic transplantation. Allogeneic transplantation is an infinitely more complicated and severe procedure. Generally, allogeneic transplants are not done on a patient over 45 or 50. The risks for this procedure are much higher than for an autologous transplant.