Dietary Supplement Use during Adjuvant Chemotherapy May Increase Risk for Breast Cancer Recurrence

SUMMARY: The Council for Responsible Nutrition reported that 77% of Americans consume dietary supplements. With the growing awareness regarding health, fitness and nutrition, the market size for dietary supplements is projected to hit a valuation of $349.4 billion by 2026.

Patients often use dietary supplements following a diagnosis of cancer, even though clinical recommendations discourage the use of antioxidant supplements during chemotherapy. One of the mechanisms of action of cytotoxic chemotherapeutic agents is through the generation of Reactive Oxygen Species (ROS). The use of dietary supplements during treatment, particularly antioxidants, could reduce the efficacy of cytotoxic agents. DELCaP study was conducted to address this concern.

DELCaP (Diet, Exercise, Lifestyle and Cancer Prognosis) trial is a prospective observational study, ancillary to an intergroup therapeutic clinical trial for high-risk breast cancer, conducted to evaluate associations between supplement use, particularly antioxidants during chemotherapy treatment, and breast cancer survival outcomes.

The Phase III SWOG S0221 trial evaluated the optimal dose and schedule of Anthracycline/Taxane adjuvant chemotherapy in women with high-risk early breast cancer. The current analysis involved a cohort of 1,134 of 2,014 patients enrolled in this study, who answered a baseline and follow-up questionnaires that included their use of dietary supplement at enrollment and during treatment. The authors then analyzed associations of dietary supplement use with clinical outcomes, after adjusting for clinical and lifestyle factors. Approximately 18% of patients used antioxidants such as Vitamins C, A, and E, Carotenoids or Coenzyme Q10 during treatment, whereas 44% of patients took multivitamins during chemotherapy.

It was noted from this analysis that the use of any antioxidant supplement (Vitamins A, C, and E, Carotenoids and Coenzyme Q10), both before and during adjuvant treatment was associated with an increased risk of recurrence versus no such use of supplements (HR=1.41; P=0.06). There was also a nonsignificant increased risk of overall mortality with the use of any antioxidant supplement (HR=1.40; P=0.14). There was a weaker relationship of outcomes with individual antioxidants and this may perhaps be due to the small numbers of patients. With regards to nonoxidants, Vitamin B12 use both before and during chemotherapy was significantly associated with poorer Disease Free Survival (HR=1.83; P<0.01) and Overall Survival (HR= 2.04; P<0.01). Use of iron during chemotherapy was also significantly associated with recurrence (HR=1.79; P<0.01), as was use both before and during treatment (HR=1.91; P=0.06). Results were similar for Overall Survival. Multivitamin use however was not associated with survival outcomes.

The researchers based on this analysis concluded that the use of antioxidant and nonantioxidant dietary supplements, but not multivitamins, before and during adjuvant chemotherapy may be associated with inferior treatment outcomes, in patients with early stage high risk breast cancer. They added that caution should be exercised by patients, when considering the use of supplements, other than a multivitamin, during chemotherapy, and patients should try to get their vitamins and minerals including antioxidants through food products..

Dietary Supplement Use During Chemotherapy and Survival Outcomes of Patients With Breast Cancer Enrolled in a Cooperative Group Clinical Trial (SWOG S0221). Ambrosone CB, Zirpoli GR, Hutson AD, et al. J Clin Oncol. 2019;38:804-814