The Potential Role of Xenobiotics
in the Etiology of Breast Cancer
Statistics indicate that the incidence of women developing cancerous breast tumors has increases significantly in recent decades (Kelsey an Horn-Ross 1993). This increased risk is especially apparent in industrialized countries but demographic studies also suggest the trend is worldwide (Magrath and Litvak 1993). Scientists disagree as to the exact mechanism that drives mammary tumor formation (Harris et al 1992; Willett 1989) but the role of estrogen is strongly implicated (Bernstein and Ross 1993).
During this same time period, two other alarming trends relating hormones and biological well-being have also been observed. The first is found in wildlife populations, many of which have suffered reproductive abnormalities, eggshell thinning, failure to maintain their populations and other physiological and behavioral abnormalities (Cox 1993). Investigations into the causes of these problems have indicated a class of human-made chemical compounds called xenobiotics (e.g., pesticides, industrial waste products and therapeutic medicines), thousands of tons of which have been released into the environment since World War II (Geiger 1993).
A second trend concerns increasing reproductive anatomical and physiological difficulties in human males. Examples of such disorders include testicular cancer, undescended testes (cryptorchidism), urethral abnormalities (hypospadias) and a drop in semen volume and sperm counts in normal adult men (Sharp and Skakkebaek 1993).
The xenobiotic hypothesis speculates that certain xenobiotic compounds, ubiquitous in the environment, and soluble in body fat, are affecting many of the above mentioned changes (Hileman 1993). A refinement of the hypothesis, called the xenoestrogen hypothesis, suggests that some xenobiotics interact with cellular receptors and either mimic or interfere with the actions of naturally-occurring estrogens. The effect of the xenoestrogen may be to target endocrine or immune functions, leading to a variety of diseases, including cancer (Coborn, vomSaal, and Soto 1993).
It is the thesis of this paper that xenobiotics, widespread in the environment, are etiological agents of breast cancer. Support for the thesis comes from epidemiological and laboratory studies, wildlife assessments and demographic data. The implications of this thesis are far-reaching and draw recommendations not only for more research, but for a change in the risk assessment methods by which suspect compounds are evaluated for toxicity.