A drug that slows cancer growth has been found to elevate the level of the hormone insulin. This insulin rise lessens the drug’s effectiveness, but a diet that lowers insulin can increase the benefits of the therapy in mice.

https://www.nature.com/articles/d41586-018-05871-x

• Hopkins and colleagues now provide evidence from mouse experiments that a diet that keeps levels of the hormone insulin low improves the effectiveness of cancer drugs that inhibit PI3K.
  • PI3K inhibitors raise blood glucose by blocking signalling downstream of the insulin receptor in tissues involved in blood-glucose regulation. 
  • insulin is secreted by the β-cells of the pancreas when blood glucose levels rise
  • cancer cells commonly also express insulin receptors, and, causes an increase in cell proliferation and a reduction in cell death, rather than affecting blood-glucose regulation.
  • a diet, low in glucose, that keeps levels of the hormone insulin low improves the effectiveness of cancer drugs that inhibit PI3K

Of course the above means that low glucose diet helps regardless if we use PI3K drugs, or not.