Supplement use, physician recommendations, and chemotherapy-induced peripheral neuropathy in a breast cancer clinical trial
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Dietary supplement use during chemotherapy is controversial, partly due to the potential effect of antioxidants on reduced efficacy of chemotherapy-related cytotoxicity. We examined supplement use among breast cancer patients registered to a clinical trial (SWOG S0221) before diagnosis and during treatment. Participants (n = 1,467) completed questionnaires regarding multivitamin and supplement use before diagnosis. Of these patients, 1,249 completed a 6-month followup questionnaire regarding supplement use during treatment. We examined the use of vitamins C, D, E, B6, B12, folic acid, and calcium at these timepoints, as well as physician recommendations regarding supplement use. The use of vitamins C, E, folic acid, and calcium decreased during treatment, while the use of vitamin B6 increased. Five hundred seventy four patients (51%) received no physician recommendations regarding supplement use. Among the remaining 49%, 10% were advised not to take multivitamins and/or supplements, 7% were advised to use only multivitamins, and 32% received recommendations to use multivitamins and/or supplements. Among patients who took vitamin C before diagnosis, those who were advised not to take supplements were >5 times more likely not to use of vitamin C during treatment than those not advised to stop use (adjusted OR = 5.27, 95% CI = 1.13-24.6). Previous non-users who were advised to take a multivitamin were nearly 5 times more likely to use multivitamins during treatment compared to those who received no recommendation (adjusted OR = 4.66, 95% CI = 2.10-10.3). As a consequence of treatment with paclitaxel, many patients develop chemotherapy-induced peripheral neuropathy (CIPN). This may lead to dose-reduction or discontinuation of therapy altogether. 1,225 SWOG S0221 participants with baseline questionnaire data received paclitaxel. Of these patients, 1,068 completed the 6-month follow-up questionnaire. We examined the use of multivitamins, vitamins C, D, E, B6, and B12, folic acid, iron, calcium, fish oil, Eicosapentaenoic acid (EPA), omega-3, flaxseed or cod liver oil, and glucosamine at these timepoints in relation to CIPN. CIPN was assessed with both the National Cancer Institute Common Toxicity Criteria for Adverse Events (CTCAE) and the Functional Assessment of Cancer Therapy/Gynecologic Oncology Group Neurotoxicity (FACT/GOG-Ntx) subscale. Using the CTCAE scale, Multivitamin use before diagnosis was associated with reduced symptoms of CIPN (adjusted OR = 0.60, 95% CI = 0.42-0.87). Although in the same direction as use prior to diagnosis, multivitamin use during treatment was less strongly associated with CIPN (adjusted OR = 0.73, 95% CI = 0.49-1.08). Utilizing the FACT/GOG-Ntx subscale, we observed similar associations, with multivitamin use before diagnosis (adjusted OR = 0.78, 95% CI = 0.61-1.00) and during treatment (adjusted OR = 0.77, 95% CI = 0.60-0.99) both associated with reduced CIPN. There were no significant associations between CIPN and any other supplement used, either before diagnosis or during treatment. In this clinical trial for high-risk breast cancer, supplement use generally decreased during treatment. Our results indicate that multivitamin use may aid in the prevention of CIPN. Upon followup from the clinical trial, findings regarding supplement use and survival outcomes will better inform physician recommendations for patients on adjuvant chemotherapy.