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 Radiologys 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, todays 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.