Birds of prey kill and regurgitate food to their young. In time they bring back injured animals for offspring to kill and eat on their own. Oncology has these two choices: killing tumor cells outright; or injuring and feeding them to a patient’s immune system.
Here I suggest that, with a high neoplastic cell count and a still healthy immune system, introducing an anti-metabolite of folic acid may work towards stimulating the latter immune response. Such conditions existed in a particular case in 2011 with some success. That success may have been lengthened, had the triweekly, anti-metabolite infusion waited an additional week, to test for this having been from an immune response. With such a response the anti-metabolite might have been suspended still longer preserving the immune system and lengthening its effectiveness. This would promise itself a chemotherapy against which no cancer could evolve towards resistance. With its occasional fresh starts and new immune responses, it would fail, if at all, with the failure of an immune response to rekindle.