Phytoestrogens and Breast Cancer
Epidemiologic evidence suggests that diet has an effect on the risk of breast cancer. Phytoestrogens (PTE) are a group of substances in foods with structure similar to estrogens. The two primary groups of PTE are isoflavonoids and lignans. Isoflavonoids are found primarily in soy products, and lignans are dominantly derived from fiber found in whole grains, berries, fruit and vegetables, and flax seed. Plant PTE are metabolized by bowel flora; the absorbed metabolites peak in 24 hours and are excreted by 48-72 hours.
Evidence that suggests a preventive capacity for PTE includes cell culture and animal experiments that demonstrate tumor inhibition. Lower incidences of breast and prostate tumors are found in Asian populations whose soy-based diet contains high amounts of PTE.
This case-control study compared 144 women with newly diagnosed early breast cancer to age and geographically matched controls. Urine samples were analyzed for PTE metabolites.
High intake of PTE (as manifest by high excretion of PTE metabolites) was associated with a substantial reduction in the risk of breast cancer; women in the top quartile of PTE excretion demonstrated a 0.27-0.36 odds ratio for breast cancer.
The authors point out that preventive efforts will be necessary to provide greatest benefit to our at-risk population. This demonstrated relationship by both observational population and case-control studies suggests that there is rationale in considering support for preferable inclusion of PTE in the diet.
Ingram D, et al. Lancet 1997;350: 990-994.
Clinical Scenario: The 12-lead tracing shown in the figure was obtained at peak exercise during a stress test performed on a 73-year-old woman. Her chief complaint was shortness of breath during activities of daily living. The exercise test was stopped at the stage shown in the figure because of chest tightness. She had just completed nine minutes on the treadmill. Despite progressively increasing her workload during the test, her heart rate had not increased over the last three stages. The blood pressure response to exercise was normal. In view of the fact that this patient is not on any rate-slowing medications and is not known to have coronary disease, how would you interpret the results?
Interpretation: The history and peak exercise tracing shown in the figure are consistent with the diagnosis of chronotropic incompetence. Although baseline artifact makes interpretation of this peak exercise tracing more difficult, it is doubtful that there is anything more than slight ST segment flattening and minimal ST depression. Instead, the most remarkable finding in this patient who is not on any rate-slowing medication is the inappropriate heart rate response to exercise.
True chronotropic incompetence (in which failure to appropriately increase heart rate with progressive exercise is not the result of effort-limiting chest pain) is a relatively uncommon phenomenon. Froehlicher suggests that patients with chronotropic incompetence represent a mixed group with several explanations for their limited heart rate response.1 These include myocardial dysfunction, coronary disease with an anginal equivalent, and a normal variant. Whether this entity reflects a manifestation of sick sinus syndrome in some individuals is uncertain. In this particular case, given the marked impairment of exercise capacity in this 73-year-old woman, cardiac catheterization should be strongly considered to define her anatomy.
Reference
1. Froehlicher VF, et al. Exercise and the Heart, 3rd ed. St. Louis: Mosby; 1993:90-91.
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