DIET, HORMONES, AND RISK OF COLORECTAL CANCER

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Colorectal cancer is the second leading cause of cancer death in the United States. Without preventive actions, approximately 6% of Americans will develop this malignancy during their lifetime. In the past several decades, there have been major developments in our understanding of three pathogenic pathways for colorectal carcinogenesis: DNA methylation aberrations, which affect gene expression and genomic stability, insulin and insulin-like growth factor (IGF) signaling, which influences cell proliferation and apoptosis, and inflammation. Many of the proposed modifiable factors for colorectal cancer (low intakes of folate, vitamin B-6 and vitamin B-12, high alcohol intake, excess body weight, sedentary lifestyle, calcium intake and vitamin D levels, and non-use of aspirin) may operate through these pathways. We propose to examine prospectively and extensively how these modifiable factors may influence colorectal cancer risk operating through these three pathways. We will utilize data from the Nurses' Health Study, a large ongoing prospective study of women. We will study relevant exposures utilizing (1) multiple questionnaires accumulated over 30 years to assess the influence of long-term exposures including diet, (2) nutrient and hormonal biomarkers, and (3) genetic factors relevant to the pathways of interest. These exposures and genetic factors will be examined in relation to various endpoints including (1) total colorectal cancer incidence, (2) specific molecular alterations in colorectal cancer (including CpG island methylation, loss of expression of hMLHt, O6-methylguanine-DNA methyltransferase, p 16K and p27, and overexpression ofphospho-Akt and COX-2), and (3) survival from colorectal cancer following a curative resection of this cancer, after accounting for know prognostic factors for this disease. By better understanding underlying mechanisms, dose-response relations, inter-relations among factors acting in similar pathways (e.g. folate and vitamin B-6, insulin and IGF-1), variation in response due to genetic susceptibility, and specificity in associations to specific tumor markers which enhances the case for causality, we can solidify and refine recommendations aimed at reducing the incidence and mortality from this largely preventable cancer.