The dissertation contains three research papers which examined the following issues in breast cancer survivors (a) the primary methodological issue among the studies addressing the use of complementary and alternative medicine (CAM),which has been to establish criteria for a meaningful definition of a CAM user, (b) the impact on breast cancer prognosis for those women who used CAM therapies as an alternative to undergoing conventional systemic treatments, which have been recommended to them and (c) the use of dietary supplements, which is the most commonly used form of CAM and potentially the most likely to interfere with cancer treatment. All three papers were secondary data analyses, using the dataset from the WHEL study, which assessed 3088 women at study enrollment. During the follow-up period, 2562 WHEL study participants completed a structured telephone interview that measured CAM use, including the modality, the purpose for the use, and the frequency. The CAM and dietary supplement use data were the focus of these research papers. The study findings have shown that (a) there are important distinctions to be made among the different classes of CAM users, (b) complementary and alternative therapies should not be used in place of standard treatment for breast cancer patients and (c) dietary supplements may improve overall micronutrient intakes but were not associated with all-cause mortality among this cohort of breast cancer survivors.