Grand Rounds

Do Dietary Supplements Interfere with Breast Cancer Treatment

BACKGROUND AND PURPOSE:

Many people report using dietary supplements during cancer treatment
- Antioxidants may interfere with the chemotherapy cytotoxicity
Ambrosone et al. (Journal of Clinical Oncology, 2019) evaluated the relationship between supplements and breast cancer outcomes

Prospective study ancillary to a therapeutic trial
Participants
- Patients with breast cancer enrolled in a trial that evaluated use of cyclophosphamide, doxorubicin, and paclitaxel
Self-reported dietary supplement use (at registration and during the trial)
- Antioxidant supplements: Vitamins A, C, and E; carotenoids | Coenzyme Q10
- Vitamin B12
- Multivitamins
- Iron
Study design and data analysis
- Cox proportional hazards regression
  - Adjusting for clinical and lifestyle variables (e.g., age, tumor characteristics etc.)
Outcomes: Recurrence and survival

1,134 patients were surveyed
Antioxidants (both before and during treatment): Trend towards increased recurrence and death with use
- Recurrence: Adjusted hazard ratio [aHR] 1.41 (95% CI, 0.98 to 2.04; P = 0.06)
- Death: aHR, 1.40; 95% CI, 0.90 to 2.18; P = 0.14
- Relationships with individual antioxidants were weaker (small numbers)
Vitamin B12 (both before and during chemotherapy): Significantly associated with decreased disease free survival and survival
- Poorer disease-free survival: aHR 1.83 (95% CI, 1.15 to 2.92; P < 0.01)
- Poorer overall survival: aHR 2.04 (95% CI, 1.22 to 3.40; P < 0.01)
Iron use (during chemotherapy): was significantly associated with recurrence
- Recurrence: aHR, 1.79; 95% CI, 1.20 to 2.67; P < 0.01
Multivitamin use was not associated with survival outcomes

Based on this prospective study, the authors advise caution and “that use of antioxidant supplements during chemotherapy, as well as iron and vitamin B12, may increase the risk of breast cancer recurrence and mortality”

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