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For Patients With Metastatic Colorectal Cancer, Diet Does Not Improve Survival

Diet quality did not improve overall survival in patients with metastatic colorectal cancer (mCRC), according to a prospective cohort study published today in JAMA Network Open.

The investigators, led by Erin Van Blarigan, Scd, Assistant Professor of Epidemiology & Biostatistics and of Urology at the University of California, San Francisco, evaluated the diet qualities of 1,284 patients with metastatic colorectal cancer from October 2005 to February 2012. The patients were enrolled into Cancer and Leukemia Group B (Alliance) and Southwest Oncology Group 80405. Four weeks after receiving first-line treatment for mCRC, patients submitted a validated food frequency questionnaire, which identified dietary habits to find commonalities with three diet quality methods. It contained 130 items concerning clinical data and lifestyle factors.

The Alternative Healthy Eating Index (AHEI) scored intake of fruits, whole grains, nuts, legumes, long-chain n-3 fatty acids, polyunsaturated fatty acids, sweetened beverages and juices, red and processed meats, trans fats, sodium, and alcoholic drinks, on a scale of of 0 to 110. The Alternative Mediterranean Diet (AMED) measured intake of vegetables, fruits, nuts, whole grains, legumes, fish, ratio of monounsaturated to saturated fat, red and processed meat, and alcohol on a scale of one to nine. The Dietary Approaches to Stop Hypertension (DASH), scored on a scale of 0 to 45, included fruits, vegetables, nuts and legumes, low-fat dairy, whole grains, sodium, sweetened beverages, red and processed meats, and sweets and desserts. Higher scores indicated more successful compliance with the dietary model.

The authors also examined two dietary patterns: the Western dietary pattern, which includes higher consumption of dairy, refined grains, condiments, red meats, and sweets and desserts, and the prudent dietary pattern, which includes high amounts of vegetables, legumes, and fruit. Dietary pattern scores were generated for each participant after three months. Higher scores indicated more favorable results.

At a median follow-up of 73 months, 1,100 patient deaths had occurred, of which 976 were attributed to colorectal cancer. The authors eliminated 135 patients who died 90 days or less after completing their food frequency questionnaire to prevent "reverse causation," when the patient changed his/her diet before they died from an underlying illness.

The investigators found no statistically significant associations between diet and overall survival. However, related to the Mediterranean diet, there was a statistically insignificant inverse association between AMED score and risk of death, with a hazard ratio of 0.83 when the fifth and first quintiles on the AMED scores were compared (95% confidence interval, 0.67–1.04; P = .04). In addition, the Western diet pattern was associated with longer survival in patients with KRAS-variant tumors, with a hazard ratio of 0.50 for the fifth verses first quintiles on this measure, but not for patients with wild-type tumors.

"Patients and clinicians often seek advice on whether diet changes or other modifiable factors can impact outcomes," comment Dr. Van Blarigan and colleagues. "Although there are increasing data on modifiable factors, such as exercise and diet, in people with colorectal cancer, there remains a paucity of data to guide patients with advanced and metastatic disease. In a recent study with this same cohort of patients, physical activity was observed to be associated with longer survival. In contrast, the current study did not find an association between overall diet quality and survival. Thus, although data are limited to one cohort so far, efforts to help patients adopt and maintain a physical activity routine may be more important than suggesting changes to their overall dietary pattern at the time of initiation of treatment for metastatic colorectal cancer."

In an invited commentary published alongside the study in JAMA Network Open, Cindy Kin, MD, Assistant Professor of Surgery at Stanford University School of Medicine, stated, "The data available for this cohort of patients allowed the authors to draw conclusions regarding the association between outcomes and diet quality before treatment. More studies are necessary for understanding the associations of diet with outcomes during and after treatment. Answering this question is critical for formulating actionable diet interventions to best support these patients through treatment and to optimize their outcomes."

For More Information For More Information

Van Blarigan EL, Zhang S, Ou FS, et al (2020). Association of diet quality with survival among people with metastatic colorectal cancer in the Cancer and Leukemia B and Southwest Oncology Group 80405 trial. JAMA Netw Open, 3(10):e2023500. DOI:10.1001/jamanetworkopen.2020.23500

Kin C (2020). Diet quality at the initiation of treatment for metastatic colorectal cancer. JAMA Netw Open, 3(10):e2023718. DOI:10.1001/jamanetworkopen.2020.23718

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