Overweight and obese women – defined as having a BMI (body mass index) higher than 25 – have a higher risk of being diagnosed with breast cancer compared to women who maintain a healthy weight, especially after menopause. Being overweight also can increase the risk of breast cancer coming back (recurrence) in women who’ve been diagnosed with the disease.
This higher risk is partially because fat cells make estrogen; extra fat cells mean more estrogen in the body and estrogen can make hormone-receptor-positive breast cancers develop and grow. Scientists also have recently found that extra fat cells can trigger long-term, low-grade inflammation in the body. Chronic inflammation has been linked to a higher risk of breast cancer recurrence; the proteins secreted by the immune system seem to stimulate breast cancer cells to grow, especially estrogen-receptor-positive breast cancer in postmenopausal women.
At the same time, dozens of studies have shown that losing weight, exercising more, and eating a healthy diet improve the physical and mental well-being of people who’ve been diagnosed with breast cancer. People who make these changes also see positive changes in biomarkers (measurable characteristics in the body) linked to breast cancer risk and outcomes.
At the 2013 American Society of Clinical Oncology Annual Meeting, several studies were presented that looked at obesity and breast cancer.
Obesity and aromatase inhibitors: Results have been mixed in studies looking at whether aromatase inhibitors are as effective for obese postmenopausal women diagnosed with early-stage, hormone-receptor-positive breast cancer as they are for women at a healthy weight. In “A meta-analysis of endocrine therapy trials in early breast cancer (BC) evaluating the impact of obesity: Are aromatase inhibitors (AIs) optimal therapy in obese ER+ BC?” the researchers did a meta-analysis on four studies involving nearly 11,400 postmenopausal women diagnosed with early-stage, estrogen-receptor-positive breast cancer looking at BMI and hormonal therapy. (A meta-analysis is a study that combines and analyzes the results of a number of earlier studies.)
The researchers found that women with a BMI greater than 25 were likely to have worse disease-free survival (the length of time the women lived without the cancer coming back) overall compared to women at a healthy weight. They also found that aromatase inhibitors were less effective in reducing the risk of breast cancer coming back in overweight and obese women compared to women at a healthy weight. More research is needed to see if one of the aromatase inhibitors is more effective than another in overweight women.
Obesity and breast cancer prognosis: Many doctors have observed that obese women diagnosed with breast cancer seem to have worse outcomes. In “The effect of obesity on prognosis in operable breast cancer patients treated with adjuvant anthracyclines and taxanes according to pathologic subtypes,” researchers wanted to see if this held true in the study and also see if the characteristics of the breast cancer affected whether obese women had worse prognoses.
The researchers looked at the results of more than 5,500 women diagnosed with breast cancer who were participating in studies looking at the effectiveness of anthracycline and taxane chemotherapy after surgery. After taking into account the women’s age and menopausal status, as well as the size of the cancer, whether the lymph nodes were involved, the type of surgery, the grade of the cancer, hormone receptor and HER2 status, chemotherapy regimen, and the possibility of undertreatment, the researchers found that women with a BMI of 35 or higher had a higher risk of recurrence, a higher risk of dying from breast cancer, and a higher risk of dying from any cause compared to healthy weight women. This held true for all types of breast cancer.
Obesity and age at diagnosis: Egypt has one of the highest obesity rates in the world for girls and women ages 15 and older. In “Obesity as a prognostic factor for incidence and survival in female patients diagnosed with breast cancer,” researchers wondered if the obesity rates were affecting the number of breast cancer cases diagnosed in the country, as well as survival.
Looking at the records of more than 900 women who were diagnosed with breast cancer from 1996 to 2005, the researchers put the women into four groups based on BMI:
- less than 18.5 (100 women)
- 18.5 to less than 25 (299 women)
- 25 to less than 30 (336 women)
- higher than 30 (172 women)
They found that overweight and obese women were overall more likely to be diagnosed with breast cancer and were more likely to be diagnosed at a younger age compared to women at a healthy weight. These heavier women also were more likely to be diagnosed with more advanced-stage cancer. Compared to women at a healthy weight, overweight and obese women also had worse disease-free survival and also had worse overall survival. As BMI went up, so did the risk of a woman dying from any cause.
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 kinds 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 following.
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 plan. And the Breastcancer.org Exercise section can help you find a trainer and learn how to stick to an exercise routine.