If a woman has been diagnosed with breast cancer, her risk of being diagnosed with a second primary cancer increases as her weight increases, according to a study.
The research was published on April 5, 2021, by the Journal of the National Cancer Institute. Read the abstract of “Body Mass Index and Risk of Second Cancer among Women with Breast Cancer.”
Links between excess weight and cancer
The International Agency for Research on Cancer has linked 13 types of cancer with being overweight and obese:
- meningioma (a type of brain tumor)
- multiple myeloma (cancer that forms in a type of white blood cell)
- adenocarcinoma of the esophagus (cancer in the cells of the mucus-secreting glands of the esophagus)
- thyroid cancer
- postmenopausal breast cancer
- gall bladder cancer
- stomach cancer
- liver cancer
- pancreatic cancer
- kidney cancer
- ovarian cancer
- uterine cancer
- colorectal cancer
Researchers know that women who have been diagnosed with breast cancer once have a higher risk of developing a second primary cancer compared to the average woman. The researchers who did this study wanted to know if excess weight affected the risk of a second cancer in women who had initially been diagnosed with breast cancer.
About the study
The study included information on 6,481 women who were diagnosed with stage I to stage III breast cancer between 2000 and 2014 in Colorado or Washington. All the women were part of the Kaiser Permanente healthcare system. The breast cancer was their first cancer diagnosis.
Women who had double mastectomy were excluded from the study.
The women’s information included the characteristics of any breast cancer diagnosed, as well as the women’s height and weight measurements from up to 2 years before diagnosis through 1 year after diagnosis.
The women’s height and weight measurements were used to calculate their BMI (body mass index), a measure of body fat based on height and weight. BMI is calculated by dividing a person’s weight by their height squared. According to the National Institutes of Health, BMI categories are:
- less than 18.5: underweight
- 18.5–24.9: normal weight
- 25–29.9: overweight
- 30 or greater: obese
While BMI can be a helpful general tool, it does have limits. It may overestimate the amount of fat in athletes and other people who are very muscular. It also can underestimate the amount of fat in older people and people who may have lost muscle mass.
The characteristics of the women in the study were:
- average age at first breast cancer diagnosis was 61.2
- 82.2% were white
- 3.4% were Black
- 62% had stage I breast cancer at first diagnosis
- 32.6% had stage II breast cancer at first diagnosis
- 5.4% had stage III breast cancer at first diagnosis
- 80% had estrogen-receptor-positive breast cancer at first diagnosis
- all had breast cancer surgery (either single mastectomy or lumpectomy)
- 70.8% were treated with radiation
- 38.2% were treated with chemotherapy
- 68.4% were treated with hormonal therapy
- 33.4% were overweight at first diagnosis
- 33.8% were obese at first diagnosis
The women were followed for about 7 years on average (ranging from 12 to 322 months).
During follow-up, 822 women (12.7%) were diagnosed with a second primary cancer. Of the secondary primary cancers:
- 333 (5.1%) were breast cancer, 231 (69.4%) of which were estrogen-receptor-positive
- 508 (7.8%) were considered obesity related. Of these cancers:
- 283 were postmenopausal breast cancer
- 70 were colorectal cancer
- 68 were endometrial cancer
- 21 were ovarian cancer
- 23 were pancreatic cancer
- 14 were kidney cancer
The researchers used statistical software to analyze any relationships between second primary cancer diagnoses and BMI.
The researchers found that as a woman’s BMI increased, so did her risk of developing a second primary cancer.
Their analysis showed that for every 5 kg (about 11 pounds) increase in weight — which means a higher BMI — a woman’s risk of a second primary cancer also increased. A higher BMI resulted in a:
- 7% greater risk of a second primary cancer
- 13% greater risk of a second primary obesity-related cancer
- 11% greater risk of a second primary breast cancer
- 15% greater risk of a second primary estrogen-receptor-positive breast cancer
“These findings have important public health implications given the number of breast cancer survivors with excess body weight,” lead author Heather Spencer Feigelson, Ph.D., senior investigator at the Kaiser Permanente Colorado Institute for Health Research, said in a statement. “Our study examined whether cancer survivors are at an increased risk of developing a second cancer and what factors contribute to this increased risk. Our findings truly underscore the need for effective weight loss prevention strategies, including nutrition and physical activity guidelines for breast cancer survivors.”
What this means for you
Losing weight can be hard, but as this study and others strongly suggest, it can be very important for your health.
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. 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 plans.
Other research suggests that it may be easier to make diet and exercise changes if you have someone to talk to you and motivate you. You might want to talk to your doctor or a registered dietitian about developing a healthy eating plan designed specifically for you and your needs.
It’s also a good idea to talk to your primary care doctor and your surgeon before you start an exercise program. Tell them the exercises you plan to do, and ask if there are any movements you should avoid or if you should limit your range of motion in any way. It’s also smart to talk about any other medical conditions you have (asthma or osteoporosis, for example) and how they may affect your ability to exercise.
Losing weight can be hard to do, but it can be done with careful diet and exercise changes. Be nice to yourself; don’t punish yourself.
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.
Written by: Jamie DePolo, senior editor
Reviewed by: Brian Wojciechowski, M.D., medical adviser
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