The practice of calorie restriction reduces the risk of suffering cancer, just as it reduces risk of suffering all other common age-related conditions. However if you do become unlucky and develop cancer, calorie restriction tends to improve the outcome, shifting the odds in your favor: there is a range of research to demonstrate that calorie restriction augments the effectiveness of cancer treatments, for example.
According to a study [the] triple negative subtype of breast cancer - one of the most aggressive forms - is less likely to spread, or metastasize, to new sites in the body when mice were fed a restricted diet. [When] mouse models of triple negative cancer were fed 30 percent less than what they ate when given free access to food, the cancer cells decreased their production of microRNAs 17 and 20 (miR 17/20). Researchers have found that this group of miRs is often increased in triple negative cancers that metastasize. This decrease in turn increased the production of proteins involved in maintaining the extracellular matrix. "Calorie restriction promotes epigenetic changes in the breast tissue that keep the extracellular matrix strong. A strong matrix creates a sort of cage around the tumor, making it more difficult for cancer cells to escape and spread to new sites in the body."
In theory, a drug that decreased miR 17 could have the same effect on the extracellular matrix as calorie restriction. However, targeting a single molecular pathway, such as the miR17 is unlikely to be as effective as calorie restriction. Triple negative breast cancers tend to be quite different genetically from patient to patient. If calorie restriction is as effective in women as it is in animal models, then it would likely change the expression patterns of a large set of genes, hitting multiple targets at once without toxicity. Breast cancer patients are often treated with hormonal therapy to block tumor growth, and steroids to counteract the side effects of chemotherapy. However, both treatments can cause a patient to have altered metabolism which can lead to weight gain. In fact, women gain an average of 10 pounds in their first year of treatment. Recent studies have shown that too much weight makes standard treatments for breast cancer less effective, and those who gain weight during treatment have worse cancer outcomes. "That's why it's important to look at metabolism when treating women with cancer."
In order to test that this hypothesis is true in humans, [the researchers are] currently enrolling patients in the CaReFOR (Calorie Restriction for Oncology Research) trial. As the first trial like it in the country, women undergoing radiation therapy for breast cancer receive nutritional counseling and are guided through their weight loss plan as they undergo their treatment for breast cancer.