The following review article from Cancer Therapy Advisor summarises three main studies of the effects of a vegan diet on the risk of developing cancer.
The article concludes that adoption of a vegan diet may reduce the risk of developing cancer, but the data are inconclusive regarding specific cancer types due to the small numbers of vegan patients in the study populations. There are no data regarding whether a vegan diet is an effective means of prevention among high-risk populations. However, there is no evidence that a vegan diet is harmful, and it may be a healthy option for patients who properly plan meals.
Patients should consult with a dietitian before following special diets to ensure the diet provides sufficient nutrition.