Commentary: Diet and Colorectal Cancer, September 2022

This month's journal articles in the field of colorectal cancer research lack the cachet of some of the high-profile dispatches we discussed in previous editions of Clinical Edge. Nonetheless, there are several interesting reports this month.

The first is a clinical trial report that came out of China investigating the possible synergistic effect of high-dose vitamin C with chemotherapy in the first-line treatment of metastatic colorectal cancer (mCRC). The study was based on preclinical data that showed a synergistic increase in cancer cell death with chemotherapy plus high-dose vitamin C in in vitro models. Wang and colleagues randomly assigned 442 treatment-naive patients with mCRC to receive folinic acid, fluorouracil, and oxaliplatin (FOLFOX) and bevacizumab with or without 1.5 g/kg vitamin C intravenously on days 1-3 of each chemotherapy cycle.

The study's primary endpoint was progression-free survival (PFS), and patients were stratified on the basis of tumor sidedness and use of bevacizumab. PFS for the intention-to-treat group was unaffected by use of vitamin C (hazard ratio [HR] 0.86; 95% CI 0.70-1.05; P = .1). However, patients whose tumors harbored RAS mutations had a PFS that was significantly improved in the vitamin C arm (9.2 vs 7.8 months; HR 0.67; 95% CI 0.50-0.91; P = .01). Additionally, treatment-related adverse events were no more common in the treatment arm than in the control arm. Although I seldom draw clinical conclusions from subgroup analyses, I find it comforting to know that high-dose vitamin C is at least safe and potentially helpful for some patients. Many of my patients through the years have asked me about the utility of high-dose vitamin C. At least I can now inform them that the treatment is unlikely to cause physical harm or substantially decrease the efficacy of chemotherapy.

The second article I will discuss focuses on dietary fat intake and its potential effects on mortality and cancer progression in patients with mCRC. Using a food-frequency questionnaire, the authors of the study assessed the diets of 1194 patients who had been part of a previous cooperative group study for patients with treatment-naive mCRC (Van Blarigan et al). Over a median follow-up of 6.1 years, patients with the highest median intake of vegetable fats (23.5% kcal/d; interquartile range [IQR] 21.6%-25.7% kcal/d) vs the lowest intake (11.6% kcal/d; IQR 10.1%-12.7% kcal/d) showed a lower risk for all-cause mortality (adjusted HR 0.79; 95% CI 0.63-1.00) and cancer progression or death (adjusted HR 0.71; 95% CI 0.57-0.88). Although this study's results were not unexpected given data that have been published in the past, it builds on previous work as it shows the specific benefits of vegetable fats vis-à-vis animal fats, which are detrimental to survival. Oncologists continue to benefit from these studies because they allow us to give more specific dietary recommendations for high fat-containing vegan foods, such as avocados, olives, and nuts.

This month's journal articles in the field of colorectal cancer research lack the cachet of some of the high-profile dispatches we discussed in previous editions of Clinical Edge. Nonetheless, there are several interesting reports this month.

The first is a clinical trial report that came out of China investigating the possible synergistic effect of high-dose vitamin C with chemotherapy in the first-line treatment of metastatic colorectal cancer (mCRC). The study was based on preclinical data that showed a synergistic increase in cancer cell death with chemotherapy plus high-dose vitamin C in in vitro models. Wang and colleagues randomly assigned 442 treatment-naive patients with mCRC to receive folinic acid, fluorouracil, and oxaliplatin (FOLFOX) and bevacizumab with or without 1.5 g/kg vitamin C intravenously on days 1-3 of each chemotherapy cycle.

The study's primary endpoint was progression-free survival (PFS), and patients were stratified on the basis of tumor sidedness and use of bevacizumab. PFS for the intention-to-treat group was unaffected by use of vitamin C (hazard ratio [HR] 0.86; 95% CI 0.70-1.05; P = .1). However, patients whose tumors harbored RAS mutations had a PFS that was significantly improved in the vitamin C arm (9.2 vs 7.8 months; HR 0.67; 95% CI 0.50-0.91; P = .01). Additionally, treatment-related adverse events were no more common in the treatment arm than in the control arm. Although I seldom draw clinical conclusions from subgroup analyses, I find it comforting to know that high-dose vitamin C is at least safe and potentially helpful for some patients. Many of my patients through the years have asked me about the utility of high-dose vitamin C. At least I can now inform them that the treatment is unlikely to cause physical harm or substantially decrease the efficacy of chemotherapy.

The second article I will discuss focuses on dietary fat intake and its potential effects on mortality and cancer progression in patients with mCRC. Using a food-frequency questionnaire, the authors of the study assessed the diets of 1194 patients who had been part of a previous cooperative group study for patients with treatment-naive mCRC (Van Blarigan et al). Over a median follow-up of 6.1 years, patients with the highest median intake of vegetable fats (23.5% kcal/d; interquartile range [IQR] 21.6%-25.7% kcal/d) vs the lowest intake (11.6% kcal/d; IQR 10.1%-12.7% kcal/d) showed a lower risk for all-cause mortality (adjusted HR 0.79; 95% CI 0.63-1.00) and cancer progression or death (adjusted HR 0.71; 95% CI 0.57-0.88). Although this study's results were not unexpected given data that have been published in the past, it builds on previous work as it shows the specific benefits of vegetable fats vis-à-vis animal fats, which are detrimental to survival. Oncologists continue to benefit from these studies because they allow us to give more specific dietary recommendations for high fat-containing vegan foods, such as avocados, olives, and nuts.

This month's journal articles in the field of colorectal cancer research lack the cachet of some of the high-profile dispatches we discussed in previous editions of Clinical Edge. Nonetheless, there are several interesting reports this month.

The first is a clinical trial report that came out of China investigating the possible synergistic effect of high-dose vitamin C with chemotherapy in the first-line treatment of metastatic colorectal cancer (mCRC). The study was based on preclinical data that showed a synergistic increase in cancer cell death with chemotherapy plus high-dose vitamin C in in vitro models. Wang and colleagues randomly assigned 442 treatment-naive patients with mCRC to receive folinic acid, fluorouracil, and oxaliplatin (FOLFOX) and bevacizumab with or without 1.5 g/kg vitamin C intravenously on days 1-3 of each chemotherapy cycle.

The study's primary endpoint was progression-free survival (PFS), and patients were stratified on the basis of tumor sidedness and use of bevacizumab. PFS for the intention-to-treat group was unaffected by use of vitamin C (hazard ratio [HR] 0.86; 95% CI 0.70-1.05; P = .1). However, patients whose tumors harbored RAS mutations had a PFS that was significantly improved in the vitamin C arm (9.2 vs 7.8 months; HR 0.67; 95% CI 0.50-0.91; P = .01). Additionally, treatment-related adverse events were no more common in the treatment arm than in the control arm. Although I seldom draw clinical conclusions from subgroup analyses, I find it comforting to know that high-dose vitamin C is at least safe and potentially helpful for some patients. Many of my patients through the years have asked me about the utility of high-dose vitamin C. At least I can now inform them that the treatment is unlikely to cause physical harm or substantially decrease the efficacy of chemotherapy.

The second article I will discuss focuses on dietary fat intake and its potential effects on mortality and cancer progression in patients with mCRC. Using a food-frequency questionnaire, the authors of the study assessed the diets of 1194 patients who had been part of a previous cooperative group study for patients with treatment-naive mCRC (Van Blarigan et al). Over a median follow-up of 6.1 years, patients with the highest median intake of vegetable fats (23.5% kcal/d; interquartile range [IQR] 21.6%-25.7% kcal/d) vs the lowest intake (11.6% kcal/d; IQR 10.1%-12.7% kcal/d) showed a lower risk for all-cause mortality (adjusted HR 0.79; 95% CI 0.63-1.00) and cancer progression or death (adjusted HR 0.71; 95% CI 0.57-0.88). Although this study's results were not unexpected given data that have been published in the past, it builds on previous work as it shows the specific benefits of vegetable fats vis-à-vis animal fats, which are detrimental to survival. Oncologists continue to benefit from these studies because they allow us to give more specific dietary recommendations for high fat-containing vegan foods, such as avocados, olives, and nuts.