Dietary supplement use during chemotherapy and survival outcomes of patients with breast cancer enrolled in a cooperative group clinical trial (SWOG S0221)

1. Certain dietary supplements, including vitamin B12, iron and omega-3 fatty acids, may negatively impact disease-free survival and overall survival in breast cancer patients undergoing chemotherapy

Evidence Rating Level: 2 (Good)

While the use of dietary supplements during cancer treatment is not uncommon, there is little data available to support current recommendations for use during chemotherapy. While supplements could reduce treatment-related adverse effects, concerns have been raised surrounding the generation of reactive oxygen species (ROS), which could affect treatment efficacy. In this observational study, 1134 patients with breast cancer that had been randomly assigned to an intergroup metronomic trial of cyclophosphamide, doxorubicin, and paclitaxel, were queried on their use of supplements at the initiation and during treatment. Researchers found that patients who used any antioxidant both before and during treatment had an increased risk of disease recurrence (HR 1.41, 95% CI 0.98 to 2.04, p=0.06) and death (HR 1.40, 95% CI 0.90 to 2.18), though these findings were not statistically significant. In examining the use of specific supplements, researchers found that the use of vitamin B12 before and during treatment was associated with poorer disease-free survival (HR 1.85, 95% CI 1.15 to 2.92) and overall survival (HR 2.04, 95% CI 1.22 to 3.40). The analysis yielded similar findings with respect to recurrence for the use of iron supplementation. The use of omega-3 fatty acids before and during treatment was associated with poorer disease-free survival (HR 1.67, 95% CI 1.12 to 2.49) but not overall survival. This study therefore shows that certain dietary supplements may negatively impact disease-free survival and overall survival. Clinicians should exercise caution in recommending particular supplements, including vitamin B12, iron and omega-3 fatty acids, to patients undergoing chemotherapy.