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Thu, Oct. 17

Breast cancer: Diagnosis, death increase with age

What can increase the risk of breast cancer for women as they get older? The American Cancer Society provides the following information.

Breast cancer incidence and death rates generally increase with age. Seventy-nine percent of new cases and 88 percent of breast cancer deaths occurred in women 50 years of age and older.

A decrease in incidence rates that occurs in women 80 years of age and older may reflect lower rates of screening, the detection of cancers by mammography before 80 years of age, and/or incomplete detection.

Based on the most recent data, relative survival rates for women diagnosed with breast cancer are:

• 89 percent at 5 years after diagnosis.

• 83 percent after 10 years.

• 78 percent after 15 years.

One should interpret relative survival rates with caution. First, they do not predict individual prognosis because many patient and tumor characteristics that influence breast cancer survival are not taken into account. Second, long-term survival rates are based on the experience of women treated many years ago and do not reflect the most recent improvements in early detection or treatment.

The 5-year relative survival rate is lower among women diagnosed with breast cancer before age 40 (85 percent) compared to women diagnosed at 40 years of age or older (90 percent). This may be due to tumors diagnosed at younger ages being more aggressive and/or less responsive to treatment.

Poverty, less education, and a lack of health insurance are also associated with lower breast cancer survival. The presence of additional illnesses, unequal access to medical care, and disparities in receipt of treatment likely contribute to differences in breast cancer survival.

High breast tissue density has been shown to be a strong, independent risk factor for the development of breast cancer. A number of factors can affect breast density, such as age, menopausal status, the use of certain drugs (such as menopausal hormone therapy), pregnancy, and genetics.

Breast density is influenced by inherited genetic factors, but decreases with age and is further reduced by pregnancy and menopause. Percent breast density is generally lower among women with higher body weight because of the higher proportion of fatty tissue.

The risk of breast cancer increases with increasing breast density; women with very high breast density have a 4- to 6-fold increased risk of breast cancer compared to women with the least dense breasts. In addition, mammographic detection of breast cancer is impaired for dense breast tissue.

Postmenopausal women with high levels of endogenous hormones (estrogen or testosterone produced naturally in the body) have about twice the risk of developing breast cancer compared to women with the lowest levels. High circulating hormone levels are associated with and may reflect the effects of other breast cancer risk factors, such as postmenopausal obesity and alcohol use.

The relationship in premenopausal women is less clear, which likely reflects the complexity of measuring hormone levels that vary during the menstrual cycle. Nevertheless, there is growing evidence linking high levels of testosterone to breast cancer risk in premenopausal women.

Women who have had more menstrual cycles because they started menstruating early (before age 12) and/or went through menopause later (after age 55) have a slightly higher risk of breast cancer. The increased risk may be due to longer lifetime exposure to reproductive hormones.

Younger age at first full-term pregnancy (less than 30 years old) and a greater number of pregnancies decrease the risk of breast cancer over the long term; however, there appears to be a transient increase in breast cancer risk following a full-term pregnancy, particularly among women who are older at first birth.

Most studies suggest that breastfeeding for a year or more slightly reduces a woman's overall risk of breast cancer. The protective effect may be greater for basal-like breast cancers. Longer duration is associated with greater risk reduction. In a review of 47 studies in 30 countries, the risk of breast cancer was reduced by 4.3 percent for every 12 months of breastfeeding.

One possible explanation for this effect may be that breastfeeding inhibits menstruation, thus reducing the lifetime number of menstrual cycles. Another possible explanation relates to structural changes that occur in the breast following lactation and weaning.

High bone mineral density in postmenopausal women has been associated with increased risk for breast cancer in many, but not all, studies. Bone density is not an independent risk factor for breast cancer, but a marker for cumulative estrogen exposure.

Recent use of menopausal hormones (also referred to as hormone therapy or HT) with combined estrogen and progestin increases the risk of developing and dying from breast cancer, with higher risk associated with longer use.

Risk is also greater for women who start hormone therapy soon after the onset of menopause compared to those who begin use later. The increased risk appears to diminish within 5 years of discontinuation of hormone use.

Obesity increases the risk of postmenopausal breast cancer. The risk of postmenopausal breast cancer is about 1.5 times higher in overweight women and about 2 times higher in obese women than in lean women.

In contrast, some studies have found that obesity protects against developing breast cancer before menopause. A large meta-analysis found that among women ages 40-49, the risk for developing breast cancer was about 14 percent lower in overweight women and about 26 percent lower in obese women compared to women who are normal weight.

Many studies have looked at whether the timing of weight gain influences breast cancer risk. Results from a study of more than 80,000 registered nurses found that women who gained 55 pounds or more after age 18 had almost 50 percent greater risk of breast cancer; a gain of 22 pounds or more after menopause was associated with an increased risk of 18 percent.

It is more difficult to examine the effect of weight loss on breast cancer because weight loss is often not sustained.

Growing evidence suggests that women who get regular physical activity have a 10-20 percent lower risk of breast cancer compared to women who are inactive, with stronger evidence for postmenopausal than premenopausal women. The benefit may be due to the effects of physical activity on body mass, hormones, and energy balance.

Although numerous studies have examined the relationship between food consumption (including fat, soy, dairy, meat, and fruits and vegetables) and breast cancer, there is no conclusive evidence that diet influences breast cancer risk.

Risk factors for men and breast cancer

Due to the infrequency of male breast cancer, much less is known about the disease than female breast cancer. Risk factors include radiation exposure, BRCA gene mutations, Klinefelter syndrome, testicular disorders, family history of male or female breast cancer, and obesity.

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