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Link Between Obesity and Worse Prognosis Isn’t Consistent

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Doctors believe that overweight and obese women have a higher risk of being diagnosed with breast cancer compared to women at a healthy weight. Research also shows that overweight and obese women who are diagnosed with breast cancer usually have a worse prognosis than women at a healthy weight.

Still, several studies show that the link between obesity and worse prognosis in women diagnosed with early-stage breast cancer isn't consistent: some of the studies suggest a link between obesity and worse prognosis and others don't. These results were presented at the 2010 San Antonio Breast Cancer Symposium (SABCS).

Each study was looking at various treatments for certain types of early-stage breast cancer. The analysis looked at the women's treatment outcomes and then looked for links between weight and prognosis.

Doctors usually use body mass index (BMI) to determine if a person is underweight, normal weight, overweight, or obese:

  • BMI lower than 18.5: underweight
  • BMI between 18.5 and 24.9: normal
  • BMI between 25 and 29.9: overweight
  • BMI 30 or higher: obese

In each study, some of the women were overweight or obese.

This type of analysis is challenging because factors other than weight can affect prognosis and these factors may be different in overweight and obese women compared to healthy weight women. So researchers might conclude that there's a link between weight and prognosis when the difference in prognosis is due to another factor. So the researchers did an adjusted analysis, a type of analysis that takes into account the differences between the women besides weight, so any links between weight and breast cancer prognosis are truly related to weight and not another factor.

Two of the studies showed that both disease-free survival (living without the cancer coming back) and overall survival rates were worse in obese, but not overweight, women, particularly women diagnosed with hormone-receptor-positive breast cancer.

One study showed worse overall survival -- but not disease-free survival -- rates in obese, but not overweight, women.

One study showed worse overall survival rates only in obese women diagnosed with hormone-receptor-positive, HER2-negative breast cancer.

One study showed no link between weight and prognosis.

While the link between weight and breast cancer prognosis wasn't consistent in the various studies, there is other evidence suggesting that excess weight may make breast cancer prognosis worse. Other research has shown that excess weight is associated with cancers that are more aggressive and more likely to recur (come back) after treatment. Excess weight also is associated with decreased treatment benefits.

Researchers don't completely understand why extra weight may be associated with these effects. One possible reason (particularly for hormone-receptor-positive breast cancers) is that extra body fat can increase estrogen levels and estrogen can make many breast cancers grow.

Many women are frustrated and unhappy because they gain weight during and after breast cancer treatment. This is especially true for women who get chemotherapy and/or hormonal therapy. Chemotherapy can cause early menopause in women who are premenopausal when diagnosed, which makes gaining weight easier. But there are other reasons women may gain weight after they're diagnosed:

  • the shock of diagnosis
  • daily routine disruptions because of doctor's appointments, treatments, etc.
  • emotional stress
  • recovery from surgery and radiation
  • juggling work and personal relationships
  • financial stress
  • less physical activity

If you've been diagnosed with breast cancer, try to make exercise and a healthy diet part of your daily routine, especially if you're overweight or obese. It may be hard to make these kind of changes if you're struggling to recover from treatment. Some women say it helps to think of eating well and exercising as important parts of their treatment plan. You might want to talk to your doctor or a registered dietitian to develop a healthy eating plan designed specifically for you and your needs. Losing weight is hard to do. But it can be done with exercise and careful diet changes. Be nice to yourself; don't punish yourself. Always tell your doctor about any new diet or exercise plans you're using.

In the Breastcancer.org Nutrition section, the Eating to Lose Weight After Treatment pages can help you assess your weight and create a healthy eating and exercise plan to reach and maintain a healthy weight.

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