Our Bodies, Ourselves (127 page)
Read Our Bodies, Ourselves Online
Authors: Boston Women's Health Book Collective
A woman living in the United States has a one in nine lifetime risk of developing breast cancer. While any woman can develop breast cancer, the chances increase with age. Breast cancer in men is extremely rare but does occur (about 1 in 100 individuals diagnosed with the disease will be male). Most breast cancer occurs in women with no family history or known genetic risk. In fact, 70 to 80 percent of women with breast cancer have none of the known risk factors besides age. Only 5 to 10 percent of cases are in women with high-risk mutations of the BRCA1 and
BRCA2 genes
. About 255,000 women per year are diagnosed with breast cancer, both noninvasive ductal carcinoma in situ (approximately 62,000) and invasive breast cancers (approximately 192,000). The National Cancer Institute estimates that there are more than 2.5 million women living with breast cancer in the United States.
Breast cancer incidence is highest in the United States and in western and northern Europe. The lowest rates are in Asia and Africa, although incidence rates have been rising in areas such as Japan, Singapore, and urban China. These regions are moving toward more Western economies and patterns of reproductive behavior. Although the influence of dietary patterns is complicated, higher caloric intake at younger ages can lead to earlier onset of menstruation, which
is
a risk for breast cancer.
PROBABILITY OF DEVELOPING INVASIVE BREAST CANCER AMONG WOMEN | ||||||||
CURRENT AGE IN YEARS | Â | RISK PER 1,000 WOMEN | ||||||
 |  | in 10 years |  | in 20 years |  | in 30 years |  | Lifetime |
30 | Â | 4 | Â | 17 | Â | 41 | Â | 123 |
40 | Â | 14 | Â | 37 | Â | 68 | Â | 120 |
50 | Â | 24 | Â | 56 | Â | 86 | Â | 109 |
60 | Â | 34 | Â | 67 | Â | 86 | Â | 91 |
70 | Â | 37 | Â | 58 | Â | â | Â | 65 |
* | ||||||||
** | ||||||||
*** |
The established risk factors for breast cancer do not account for all of the breast cancer cases. Despite the billions of dollars spent on breast cancer research, we have much to learn about why some women develop breast cancer and others don't.
Starting in the 1970s, the incidence of breast cancer rose at alarming rates. Much of this long-term increase is believed to be due to delayed childbearing and having few children. Obesity is also a factor. And as more women have screening mammograms, more cases are found; that accounts for some of the increase.
Between 2002 and 2003 there was a decrease in the incidence of breast cancer, particularly among women ages fifty to sixty-nine. This drop in the number of breast cancer cases coincides with the release of research findings from the Women's Health Initiative study (nhlbi.nih.gov/whi), which prompted many women to discontinue their use of hormone therapy.
Many people believe that the industrial processes and environmental damage that began during or after World War II play a major role in rising rates of breast cancer in Western countries. Research into environmental connections to breast cancer is the focus of organizations and foundations such as Silent Spring Institute (silent spring.org). Such research is difficult and frustrating because it entails identifying geographic breast cancer patterns in a population that is very mobile and hard to track.
Reproductive hormones play a role in the development of breast cancer because they can affect cell growth as well as promote the growth of an existing cancer. As women age, the effect of estrogen on breast tissue decreases. As we go through perimenopause and become postmenopausal, breast tissue changes to fat.
On mammograms, young normal breast tissue appears thick and white, but as the breast ages and turns to fat, it shows up dark on breast imaging. In part, this accounts for why breast cancers, which appear white on a mammogram, are more easily detectible in women after fifty, who are usually approaching completion of perimenopause. As Dr. Susan Love has commented, “Looking for cancer on a young woman's mammogram [is] like looking for a polar bear in the snow.”
6
Having denser breastsâwith more
glandular tissue in relation to fatty tissueâis a risk factor for the development of breast cancer. More research is being done to try to figure out why dense breast tissue is a risk factor and what, if anything, can be done for women with dense breasts.
The Women's Health Initiative (WHI) was the first randomized controlled study looking at women and hormone therapy (HT, formerly called hormone replacement therapy or HRT). It began in 1991 with the first results released in 2002 (see nhlbi.nih.gov/whi for more information). The major objectives of the WHI were to study cancer, osteoporosis, and heart disease among older women. The trial was stopped early in 2002 when researchers found that women who had taken a particular estrogen and progestin had a greater incidence of several diseases compared with women receiving a placebo.
For healthy women who took estrogen plus progestin, the research demonstrated an increased risk of heart attack, stroke, blood clots, and breast cancer. This same group also had a decreased risk of colorectal cancer and fewer fractures. After 2002, hormone therapy use declined in the United States and around the world. Many believe that this decline explains in large part the decline in incidence of breast cancer shortly afterward.
In 2006, the National Cancer Institute reported on the Women's Intervention Nutrition Study (WINS), which included women who had undergone hysterectomy and were given estrogen without progestin. (Women with a uterus who take hormones usually include a form of progesterone along with the estrogen, to reduce the chances that estrogen “unopposed” will lead to endometrial cancer.) Results from this study comparing women receiving estrogen with women receiving a placebo found that there was no difference in the risk of heart attack, but there was an increased risk of stroke and blood clots among the estrogen group. The effect on the risk of developing breast cancer was uncertain. (Estrogen made no difference in risk for colorectal cancer, but there was a reduced risk of bone fractures in women who took it.) The Million Women Study conducted in the United Kingdom
7
did show a clear increase in breast cancer among women on estrogen alone.
Follow-up studies have shown that the increased risk for breast cancer with hormone therapyâincluding both estrogen and progestinâdiminishes within five years of discontinuing hormones. Recent studies report that the breast cancers developing in women taking both estrogen and progestin are more aggressive and more lethal than doctors previously thought.
What all of this means for women is that long-term use of hormones (greater than five years) increases breast cancer risk.
8
Each woman needs to discuss hormone use with her health care provider to determine what makes the most sense for her own situation. Some women consider using bioidentical hormones as an alternative to conventional hormones. Bioidentical hormones are chemically identical to the hormones produced by your body; there are many FDA-approved hormones that fit the definition of bioidentical, and their long-term safety has yet to be established. (See
Chapter 20
, “Perimenopause and Menopause,” for more discussion.)
Breast cancer develops when changes occur in genes in breast cells. In that sense, all breast cancer has a genetic element. But genetic does not mean inherited. Only an estimated 5 to 10 percent of breast cancer cases result from an inherited genetic predisposition. In other words, more than 90 percent of all breast cancer cases result from factors that are not inherited and, in many cases, are unknown.
CAN BREAST CANCER RISK BE REDUCED?
Even though the causes of most breast cancer are unknown and nothing is guaranteed to prevent cancer, some studies have shown that certain health behaviors are associated with lower risk:
⢠Using hormone therapy during perimenopause only if needed and for a limited time (excellent evidence)
⢠Breastfeeding: the longer we nurse, the more protective the effect against premenopausal breast cancer (strong evidence).
⢠Delaying menstruation in girls by avoiding excessive caloric intake and increasing exercise in prepuberty (good to strong evidence). Girls used to start menstruating on average around age sixteen, a century ago; now the average age is around twelve, with some girls starting younger.
⢠Getting more than three hours of exercise every week (good evidence)
⢠Limiting alcohol to no more than one drink a day (good evidence)
⢠Limiting postmenopausal weight gain (good evidence)
⢠Eating more fruits and vegetables (evidence for direct connection is mixed)
⢠Consuming less saturated and trans fats, which are associated with health problems (evidence for direct connection is mixed)
Silent Spring (silentspring.org) and other environmental and health organizations have pointed to a growing body of evidence linking breast cancer to exposures to environmental pollutants and toxins. They recommend precautionary measures such as these:
⢠Microwave in glass or ceramics, not plastic. Don't let plastic food wraps touch high-fat foods such as cheese or meats during heating.
⢠Avoid plastic containers and bottles that contain endocrine disruptorsâchemicals that disrupt the endocrine system in animals, such as bisphenol A (BPA).
We all inherit half our genes from our mother and half from our father. There are some genes that dramatically increase the risk of breast cancer. Two of them are called BRCA1 and BRCA2 gene mutations. Blood tests have been developedâand are now aggressively marketed commerciallyâthat can identify these mutations. A positive test result (having one of these mutations) does
not
mean that an individual will definitely develop breast cancer. Nor does a negative test mean that a woman
won't
develop breast cancer; it means only that her lifetime risk is the same as that of most other women in the industrialized world. But for those individuals who have an inherited BRCA1 or BRCA2 mutation, there is a significantly increased lifetime risk of developing breast, pancreatic, and ovarian cancers. BRCA1 carriers have an average cumulative breast cancer risk (up to age seventy) of 65 percent, compared with 45 percent for BRCA2 carriers.
ENVIRONMENTAL POLLUTION AND BREAST CANCER
Despite our decades-old war on cancer, women today are much more likely to develop breast cancer than any previous generation
.
âSilent Spring Institute
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The consistent link between estrogen and breast cancer is one reason that scientists and activists continue to call for more research into environmental connections to cancer. The decline in breast cancer incidence that followed women's reduced use of hormone therapy strengthens the hypothesis that exposure to other external hormones and hormone-mimicking chemicals increases the risk of breast cancer. The Silent Spring Institute is a well-recognized research foundation that specifically focuses on the impact of environmental exposures, especially the effects of pollutants that mimic or disrupt estrogen and other reproductive hormones.
Even with strong evidence that chemical pollutants may affect breast cancer risk, it's difficult to apply what is learned in the laboratory setting to studies of girls and women. For one thing, it would be unethical to design a study where half of the participants were exposed to a chemical and the others were not, just to find out whether it caused cancer. Also, researchers need to be able to estimate a woman's exposures to multiple chemicals dating back to the years when a tumor started. We can't really know what's in our processed food and drinking water, what's off-gassing from the new carpet, or what's being tracked into homes from the outdoors. Finally, corporations hesitate to fund research unless patentable chemotherapies or medical procedures are likely to emerge from it. Public and philanthropic support is needed to fund environmental studies investigating underlying problems and their relation to cancer.
To find out how you can get involved with a breast cancer or environmental advocacy organization and make a difference for future generations, see
Chapter 25
, “Environmental and Occupational Health,” and
Chapter 27
, “Activism in the Twenty-first Century.”
It's important to consider the family history of breast and ovarian cancer from both your mother's and your father's sides of the family. Genetic testing should be considered only in limited circumstances.
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It is usually recommended that individuals with breast and/or ovarian cancer undergo testing for BRCA mutations because if the results are negative, their children would not need to be tested. Individuals without breast and/or ovarian cancer who are most likely to benefit from genetic testing are those of us who believeâbecause of a family history of two or more first-degree relatives (such as a mother or sister) with breast and/or ovarian cancerâthat we may be mutation carriers and, if so, who want to take some action to try to reduce our cancer risk.
