Trends in the Epidemiology of Breast Cancer Are Encouraging

WASHINGTON--Though the number of new breast cancer diagnoses has risen steadily in the United States for several years--now reaching approximately 200,000 a year--epidemiologic analysis reveals a number of hopeful trends, said Robert A Smith, PhD, senior director of detection programs for the American Cancer Society, Atlanta.

Speaking at the American College of Radiology’s 28th National Conference on Breast Cancer, he noted that continuing numerical increase in this age-specific disease does not reflect an increasing age-adjusted incidence but, rather, the doubling of the female population aged 30 to 80 that will occur between 1960 and 2020.

Compared with the situation 15 years ago, today’s cancers are found at smaller sizes and earlier stages, he said. In 1994, 54% percent of breast cancers were diagnosed in situ or at stage 1, compared with 31% in 1983. Ductal carcinoma in situ (DCIS), technically a "precancerous" condition, Dr. Smith said, now ranks as the fourth most common cancer diagnosis in American women.

Survival rates at 5, 10, and 15 years have increased steadily, which, because of earlier diagnosis, represent a real lengthening of life. And recent years have seen the first mortality drop among breast cancer patients in 50 years, he noted. Between 1991 and 1995 alone, breast cancer mortality declined 6%, initially in young and white women and now also among minorities.

Despite a widespread impression to the contrary, Dr. Smith continued, many of the most widely known modifiable risk factors for breast cancer--including early menarche, late menopause, postmenopausal obesity, and hormone replacement therapy--do not raise incidence very much, except in women at very high genetic risk.

The relative risks of these factors may appear impressive, Dr. Smith said, but the absolute risk of breast cancer--which he defined as the underlying probability of getting the disease over a specific time span--is not great even into late middle age for women without a positive family history.

For the 10 years between ages 40 and 50, an average woman has a 1.5% chance of getting breast cancer, which rises to 2.3% in the years between ages 50 and 60.

Modifiable factors that do have significant protective effects in average-risk women are early age at first birth, lactation, and physical activity. But "reproductive decisions are made in a social context," he noted, in which considerations of breast cancer risk generally play a very small role, and the "protective role of childbirth is gone by age 30."

Regular, vigorous exercise can have up to a 60% protective effect on women under age 40, he added.

For women from high-risk families, however, some risk factors act differently than in the general population. Early birth, for example, increases rather than reduces risk for these women.

Modifiable Risk Factors

Modifiable factors that increase risk include alcohol consumption and use of hormone replacement therapy after menopause. Consuming between 30 and 60 grams of alcohol a day--about 2.3 to 4.5 beers, 2.8 to 5.6 glasses of wine, or 2 to 4 shots of whisky--significantly increases risk. Hormone replacement therapy appears to increase risk somewhat for present users but to have no long-term effect after use stops.

The best predictors of breast cancer, Dr. Smith said, are family history, personal history of breast cancer, and biopsy-confirmed benign tumors. The "best advice," he said, is to reduce alcohol, maintain a desirable weight, and exercise regularly.