The latest on preventing breast cancer

One out of every eight women will be diagnosed with breast cancer in her life­time. Five-year survival rates are good (85 to 99 percent) unless tumors have metastasized (falls to 25 percent). Death rates have dropped since  1989, but nowhere near enough.

“What’s changed in the last few years is a greater emphasis on cancer subtypes,” says Regina Ziegler of the Division of Cancer Epidemiology & Genetics at the National Cancer Institute. “Researchers wonder if different subtypes have distinct causes.”

Risk of Breast Cancer

estrogen receptors

Some breast tumors have estrogen receptors (the tumors are called estrogen-positive) and some don’t (estrogen-negative). “The percentage of breast cancer that’s estrogen-negative is higher in younger than in older women,” notes Ziegler. And those tumors are typically harder to treat.

Different risk factors may fuel breast tumors depending on whether they’re estrogen-positive or estrogen-negative.

“Being overweight or obese is a stronger risk factor for estrogen-positive cancer,” notes Ziegler. Among postmenopausal women who take no hormones, those who are overweight or obese have nearly double the risk of estrogen-positive breast cancer compared to similar women who are lean. Those heavier women, however, have only a 60 percent higher risk of estrogen-negative breast cancers.

It’s not clear how extra pounds boost the odds of postmenopausal breast cancer. “For a long time, people thought that increased estrogen levels in the breast were the main explanation,” says Ziegler.

After menopause, fat cells, not ovaries, are the chief source of estrogen. “If you have more fat cells, they produce more estrogen, and estrogen stimulates breast cell proliferation,” she explains. “But people now believe that insulin and possibly inflammation also play a role.”

For example, a recent study found that women who had high insulin levels had double the risk of breast cancer, whether or not they were overweight. Still, adds Ziegler, “you’re more likely to have high insulin levels if you’re heavier and inactive.”

the influence of diet

“Alcohol is also a stronger risk factor for estrogen-positive cancer,” says Ziegler. In one recent study, women who drank one to six servings of alcohol a week had a 29 percent higher risk of estrogen-positive cancer than women who never drank alcohol. Those who drank at least seven servings a week had a 48 percent higher risk. But there was no link with the less common estrogen-negative tumors.

In contrast, “eating more fruits and vegetables, especially vegetables, may be protective for estrogen-negative tumors,” says Ziegler. When researchers pooled data from 20 studies on roughly 993,000 women, women who ate the most vegetables had an  18 percent lower risk of those tumors than women who ate the least.

exercise

Exercise seems to lower the risk of both estrogen-positive and estrogen-negative breast cancer. “With physical activity, the big question is whether it reduces risk beyond its influence on weight gain,” says Ziegler. “We don’t know.”

you have a higher risk of breast cancer if you:

  • are a woman 65 or older
  • have a relative—especially a mother, sister, or daughter—who had breast cancer
  • have mutations in genes (like BRCA1 and BRCA2) found in families with high rates of breast cancer
  • had menstrual periods that began before age  12 or menopause that began after 55
  • were older than 30 when you had your first child
  • never gave birth
  • took hormones after menopause
  • have dense breast tissue (seen on a mammogram)
  • have abnormal breast cells (atypical hyperplasia or carcinoma in situ)

warning signs: a painless lump in the breast or underarm area. Less common symptoms: thickening, swelling, distortion, tenderness, skin irritation, redness, scaliness, dimpling, puckering, pitting, discharge, or nipple turned inward.

To reduce your risk of any cancer:

  • Don’t use tobacco
  • Lose (or don’t gain) excess weight
  • Limit red and processed meat
  • Limit alcohol to 2 servings a day (men) or as little as possible (women)
  • Get at least 30 minutes of exercise a day

Sources: Breast Cancer Res. 14: R76, 2012; Am. J. Epidemiol. 180: 705, 2014; J. Natl. Cancer Inst. 105: 219, 2013; Arch. Intern. Med. 170: 1758, 2010; Cancer Res. 75: 270, 2015.

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