There was also a study that showed that chemotherapy efficacy was enhanced by fasting before treatment.
It seems that when calories are scarce, healthy cells turtle up while cancer cells keep consuming, so fasting reduces absorption rates in healthy tissues and thus collateral damage.
Healthy cells CAN turtle-up, whereas cancer cells engage in unregulated reproduction. Also, some cancer cells can only consume glucose. Which, in a fasted state, would mean that the majority of energy would be in ketones(if the individual were metabolically healthy), starving the cancer cells to death.
Because the cancers cells adapt! (fast reproduction and high mutation rate of the cancerous cells make that process quicker than antibiotics resistance)