A study found that overweight or obese Danish women diagnosed with breast cancer had a worse prognosis than women at a healthy weight. These results were reported at the 2009 San Antonio Breast Cancer Symposium.
Women who were obese at the time of diagnosis were more likely to:
- die from breast cancer
- have the cancer spread (metastasize) to parts of the body away from the breast
Women who were overweight but not obese at the time of diagnosis had similar increases in risk.
Women at a healthy weight were more likely to benefit from chemotherapy and hormonal therapy medicines given to reduce the risk of the cancer coming back.
This very large study was done in Denmark and looked at the weight and medical records of 19,000 women diagnosed with breast cancer between 1977 and 2006. A woman's weight was classified by body mass index (BMI). BMI uses your weight and height to determine if you're underweight, normal weight, overweight, or obese.
- BMI below 18.5 is underweight
- BMI between 18.5 and 24.9 is normal
- BMI between 25 and 29.9 is overweight
- BMI of 30 or higher is obese
Compared to normal weight women, women who were overweight or obese were diagnosed with cancers that:
- tended to be larger
- were more likely to have spread to the lymph nodes or spread more deeply into breast tissue
- were more likely to be higher grade (higher grade breast cancers tend to be more aggressive)
- were more likely to spread to a location away from the breast (distant metastasis) 5 years after diagnosis
- the risk of distant metastasis was 42% higher in overweight women and 46% higher in obese women compared to normal weight women
Compared to normal weight women, obese women had an 11% greater risk of dying from breast cancer during the 10 years after diagnosis. The risk of dying from breast cancer more than 10 years after diagnosis was also greater for obese and overweight women. Compared to normal weight women:
- overweight women had a 26% higher risk
- obese women had a 38% higher risk
Overweight and obese women didn't respond as well to treatment compared to normal weight women. Normal weight women had the best response to adjuvant chemotherapy and hormonal therapy (treatments given after surgery to reduce the risk of the cancer coming back). Normal weight women were 77% more likely to benefit from chemotherapy and 57% more likely to benefit from hormonal therapy compared to women who were obese, after 10 years of follow-up.
This study strongly suggests that being overweight or obese makes breast cancer prognosis worse. Excess weight is associated with more aggressive cancers and a decrease in treatment benefits. Researchers don't completely understand why extra weight is associated with these effects. One possible reason is the effect body fat has on the hormone estrogen. Extra body fat can increase estrogen levels and estrogen can make 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, which makes it much easier to gain weight. But there are other reasons women gain weight after diagnosis:
- the shock of diagnosis
- daily routine disruptions because of doctor's appointments, treatments, etc.
- emotional stress
- recovering from surgery and radiation
- juggling work and personal relationships
- financial stress
- being less physically active
If you've been diagnosed with breast cancer, try to make exercise and a healthy diet part of your daily routine, especially if you are 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 asses your weight and create a healthy eating and exercise plan to reach and maintain a healthy weight.