Question

Cohort Study

You are an epidemiologist working for the National Cancer Institute. You are asked to design a cohort study to examine the relationship between dietary intake of soy protein and risk of breast cancer.

Background

Phytoestrogens are a group of plant-derived substances that are structurally or functionally similar to estradiol. There has been much interest in the potential role of phytoestrogens in cancer prevention. Epidemiological data suggest that phytoestrogens may protect a woman from developing breast cancer, and there are some supporting clinical data, but they are far from conclusive. However, some studies have suggested that breast cancer risk increases with increased duration of vegetarianism. In addition, there is some evidence that genistein, the most prevalent isoflavone in soy, can stimulate estrogen receptor-positive (ER+) breast cancer and interfere with the anti-tumor activity of tamoxifen at low levels. (Duffy and Cyr J Womens Health. 2003. 12:617-31 and Willet Am J Clin Nutr 2003. 78(3 Suppl):539S-543S)

Design a cohort study to answer the question: What is the association between dietary intake of soy protein and risk of breast cancer?

What group of women would you choose as your exposed? Where would you find them?

What group(s) of women would you choose as your unexposed? Where would you find them?

How would you collect information on exposure (dietary intake of soy)? For example, pre-existing records, self-reporting, direct measurements, surveys, etc.

How would you collect information on the outcome (breast cancer)? For example, pre-existing records, self-reporting, direct measurements, surveys, etc.

Would you use a prospective or retrospective cohort design? Please justify your choice.

Answer 1

1. Eating a high diet containing high soya may decrease the risk of breast cancer due to the presence of phytoestrogens that mimics estrogens in the body
2. The exposed persons may be women diagnosed with an incident breast cancer and are conducted in three racials and for pre and post menopausal women (latina, african-americans and caucasian) who are taking soya as adietary factor
3. The un exposed persons are normal women who are taking soya (latina,african-american,causasian)
4. We can collect the infirmation with pre exisiting records and surveys