Breast Cancer & Estrogen & Oncogenes In recent years, major advances have

A. Breast Cancer: Estrogen and Oncogenes

Broadly defined, cancer can be characterized as a disorder of cellular proliferation. Cell growth and cell differentiation are dynamic, highly regulated processes (56:3). The involved physiologic mechanisms result in an enormous diversity of cellular structure and function. Among the higher organisms, this diversity is necessary for normal homeostasis and must be achieved through properly timed cell growth. Cells must respond appropriately to both external and internal signals (37:23). In cancer, cellular controls over growth and differentiation are disrupted. As a response to changes in their genetic material, cells just simply continue to proliferate. In the early stages of a cancerous disease process, neoplastic cells accumulate in excessive numbers at their site of origin (18:16). The simplest model for tumor development involves a single cell which acquires some grow

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nterrelated variables: (1) total estrogen exposure; (2) exposure to the bioavailable or free fraction of estradiol; or (3) exposure to estrogen plus progesterone. In addition, an "estrogen window" hypothesis has also been formulated. This states that environmental carcinogens are most potent at times when estrogen stimulation is unopposed by progesterone. According to this theory, there are two intervals in a woman's life when breast cancer risk is especially great: (1) just before menarche; and (2) during the perimenopausal period (10:821). Both of these periods are characterized by the presence of plasma estrogens, with concomitant low levels of progesterone. Despite the clear association between hormones and breast cancer, however, investigations involving blood and urine hormone levels have provided no clear associations with regard to carcinogenesis. Fishman et al. (1978, 1979) studied hormone levels throughout the menstrual cycles of 30 young women at high risk for breast cancer. It was found that the subjects' plasma levels of prolactin, luteinizing hormone, follicle-stimulating hormone, estradiol, and estrone showed no significant differences as compared to those of a control group. It was observed though that
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Approximate Word count = 9254
Approximate Pages = 37 (250 words per page)