Patients with prostate cancer who reported the highest amounts of plant-based foods in their diets had a 52% lower risk of disease progression and a 53% lower risk of recurrence compared with those who had the lowest amounts of plants in their diets. The diet assessments were based on questionnaires of food consumption given to patients enrolled in the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) study. The study will be presented by Liu et al at the 2023 ASCO Genitourinary Cancers Symposium (Abstract 392).

Background

In 2023, an estimated 288,300 new cases of prostate cancer will be diagnosed in the United States and 34,700 people will die from the disease. Risk factors for prostate cancer include older age, African ancestry, a family history of the disease, and certain inherited genetic conditions. Smoking and excess body weight may increase the risk of aggressive or deadly disease.

“While not all diets are equal in terms of modifiable risk factors for prostate cancer progression, we hope these results guide people at risk to make better, more healthful choices across their entire diet,” stressed lead study author Vivian N. Liu, BS, a clinical research coordinator and MAS candidate at the Osher Center for Integrative Health at the University of California, San Francisco. “We’ve known that diets that include vegetables, fruits, legumes, and whole grains are associated with numerous health benefits, including a reduction in diabetes, cardiovascular disease, and overall mortality. We can now add benefits in reducing prostate cancer progression to that list,” she highlighted.

CaPSURE Diet and Lifestyle Substudy

Decades of observational studies have found that foods such as tomatoes appear to reduce prostate cancer incidence and mortality. However, less is known about plant-based dietary patterns and prostate cancer survivorship, which is why the CaPSURE Diet and Lifestyle (CDL) substudy was started in 2004. Participants who were enrolled in CaPSURE and completed a diet and lifestyle questionnaire comprised the analysis population.

All of the study participants had early to mid-grade prostate cancer. They completed food frequency questionnaires about how much and how often they consumed approximately 140 different foods and beverages. The diet indices (an overall plant-based index and a healthful plant-based index) were scored based on a composite sum of positive or negative values assigned to plant-based or animal-based food groups in the diet.

The investigators adjusted for days diagnosed until the first questionnaire was given, age at diagnosis, year diagnosed, total energy intake, CaPSURE clinical site, race, walking pace, smoking status, Gleason risk score at diagnosis, prostate-specific antigen level at diagnosis, and primary treatment. The researchers also inquired about various factors that could bias the assessments—including smoking status, walking pace, history of diabetes, family history of prostate cancer, household income, education level, height, body mass index, alcohol use, multivitamin use, calcium supplement use, and selenium supplement use. These variables did not influence the results of analyses examining plant-based diets in relation to risk of prostate cancer progression. The rationale for assessing walking pace was that in past studies in this group, walking pace had been a significant predictor for disease progression, along with clinical factors such as age and disease stage and grade.

Key Findings

Among the 2,038 patients involved in the study, 10% of them (n = 204) experienced disease progression over a median of 7.4 years of observation. Participants who reported diets that included the highest amounts of plants had a 52% lower risk of disease progression and a 53% lower risk of recurrence compared with those whose diets incorporated the lowest amounts of plants. Associations did not vary by the participants’ age, walking pace, grade at diagnosis, or cancer stage at diagnosis.

Next Steps

The researchers plan to analyze plant-based diets in relation to prostate cancer–specific mortality. They will also examine plant-based dietary measures in relation to prostate cancer–specific quality of life at 2, 5, and 10 years from diagnosis.

ASCO Perspective

“The risk of disease progression is one of many pivotal concerns for [patients] with prostate cancer, as well as their family, caregivers, and physicians. These findings may directly inform clinical care, such as providing diet recommendations for managing health, and potentially offer other positive health benefits for preventing numerous chronic diseases,” concluded Bradley Alexander McGregor, MD, Clinical Director of the Lank Center of Genitourinary Oncology at the Dana-Farber Cancer Institute, an oncologist at Brigham and Women’s Hospital, as well as an ASCO Expert in genitourinary cancers.

Disclosure: For full disclosures of the study authors, visit coi.asco.org.