DISCUSSION
The purpose of this case report is to describe whether a patient receiving active cancer treatment was able to tolerate the ketogenic diet in conjunction with chemotherapy or immunotherapy. Most literature published on the subject evaluated the tolerability and response of the ketogenic diet after the failure of standard therapy. Our patient was diagnosed with stage III mucinous colon adenocarcinoma. He received adjuvant chemotherapy but quickly developed metastatic disease to the pancreas and omentum. We started him on encorafenib and cetuximab based on the BEACON study that showed improvement in response rate and survival when compared with standard chemotherapy for patients with BRAF V600E mutation.5 Unfortunately, his cancer quickly progressed within 4 months and again did not respond to pembrolizumab despite MSI-H, which lasted for another 4 months.
We suggested the ketogenic diet and the patient agreed. He started the diet along with trifluridine/tipiracil, and bevacizumab in January 2021. The patient’s metastatic cancer stabilized for 9 months until his disease progressed again. He was started on doublet immune checkpoint inhibitors ipilimumab and nivolumab based on his MSI-H and high tumor mutation burden with the continuation of the ketogenic diet until now. The CheckMate 142 study revealed that the combination of ipilimumab and nivolumab in patients with MSI-H previously treated for metastatic colon cancer showed some benefit.6
Our patient had the loss of nuclear expression of MLH1 and PMS2 (zero tumor stained) but no evidence of the loss expression of MSH2 and MSH6 genes (99% tumor stained). About 8% to 12% of patients with metastatic colon cancer have BRAF V600E mutations that are usually mucinous type, poorly differentiated, and located in the right side of the colon, which portends to a poor prognosis. Tumor DNA mismatch repair damage results in genetic hypermutability and leads to MSI that is sensitive to treatment with checkpoint inhibitors, as in our patient. Only about 3% of MSI-H tumors are due to germline mutations such as Lynch syndrome (hereditary nonpolyposis colorectal cancer). The presence of both MLH1 hypermethylation and BRAF mutation, as in our patient, is a strong indication of somatic rather than germline mutation.7
GKI, which represents the ratio of glucose to ketone, was developed to evaluate the efficacy of the ketogenic diet. This index measures the degree of metabolic stress on tumor cells through the decrease of glucose levels and increase of ketone bodies. A GKI of ≤ 1.0 has been suggested as the ideal therapeutic goal for cancer management.8 As levels of blood glucose decline, the blood levels of ketone bodies should rise. These 2 lines should eventually intersect at a certain point beyond which one enters the therapeutic zone or therapeutic ketosis zone. This is when tumor growth is expected to slow or cease.9 The patient’s ketone (β-hydroxybutyrate) level was initially high (0.71 mmol/L) with a GKI of 8.2. (low ketotic level), which meant he tolerated a rather strict diet for the first several months. This was also reflected in his 18 lb weight loss (almost 10% of body weight) and cancer stabilization, as in our previous publication.1 Unfortunately, the patient was unable to maintain high ketone and lower GKI levels due to fatigue from depleted carbohydrate intake. He added some carbohydrate snacks in between meals, which improved the fatigue. His ketone level has been < 0.5 mmol/L ever since, albeit his disease continues to be stable. The patient continues his daily work and reports a better QOL, based on the ECOG QLC-C30 form that he completed every 3 months.10 Currently, the patient is still receiving ipilimumab and nivolumab while maintaining the ketogenic diet with stable metastatic disease on PET/CT.
Ketogenic Diet and Cellular Mechanism of Action
PI3K/Akt (phosphatidylinositol-3-kinase) signaling is one of the most important intracellular pathways for tumor cells. It leads to the inhibition of apoptosis and the promotion of cell proliferation, metabolism, and angiogenesis. Deregulation of the PI3K pathway either via amplification of PI3K by tyrosine kinase growth factor receptors or inactivation of the tumor suppressor phosphatase and tensin homolog (PTEN), which is the negative regulator of the PI3K pathway, contributes to the development of cancer cells.11
A study by Goncalves and colleagues revealed an interesting relationship between the PI3K pathway and the benefit of the ketogenic diet to slow tumor growth. PI3K inhibitors inhibit glucose uptake into skeletal muscle and adipose tissue that activate hepatic glycogenolysis. This event results in hyperglycemia due to the pancreas releasing very high levels of insulin into the blood (hyperinsulinemia) that subsequently reactivate PI3K signaling and cause resistance to PI3K inhibitors. The ketogenic diet reportedly minimized the hyperglycemia and hyperinsulinemia induced by the PI3K inhibitor and enhanced the efficacy of PI3K inhibitors in tumor models. Studies combining PI3K inhibitors and ketogenic diet are underway. Hence, combining the ketogenic diet with chemotherapy or other novel treatment should be the focus of ketogenic diet trials.12,13