A retrospective analysis of five children with tuberous sclerosis on a ketogenic diet because of untreatable epilepsy did not reveal any influence on brain tumors (24).
A case report of two children with brain tumors on a ketogenic diet describes a reduction of glucose uptake in PET-CT. One girl survived for several months without progression (25).

In an older study, a ketogenic diet with high amounts of omega-3-fatty acids was fed enterally to patients with cachexia from cancer.
The authors did not describe a positive effect on cachexia or on the course of disease (26).

Pre-clinical data are ambiguous.
Some show a reduction of tumor. Yet some in vitro as in vivo experiments, gave warnings as to the safety of this diet. In vitro data showed that cancer cells not only adapt to the situation but develop mutations and characteristics of stem cells.
One hypothesis is that the diet puts the tumor under stress and thus selects for resistance and malignancy.
In an experiment on mice, the tumors in the diet-treated group initially grew less but later tumor growth accelerated and exceeded that of the control group (28, 29, 30, 31).

Other experiments show that a reduction of tumor growth is seen if the animals lose weight – independent from the kind of diet (32).