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.
Statistics show that more than 66% of U.S. women are overweight or obese, which puts them at higher risk for breast cancer.
A Swedish study suggests that besides having a higher risk of breast cancer, overweight and obese women are more likely to have larger breast cancer tumors at diagnosis. The researchers said this may mean that overweight and obese women should have more frequent screening so the cancers can be found when they are smaller.
The study was presented on Nov. 29, 2017 at the 2017 Radiological Society of North America annual meeting. Read the abstract of “Large Breast Cancers in Women Attending Regular Screening: Risk Factors and Implications for Prognosis.” (PDF)
While studies have questioned the value of screening mammograms, many organizations, including Breastcancer.org, recommend that screening mammograms be done annually and start at age 40. In Sweden, women ages 50 to 69 have mammograms every 2 years and women ages 40 to 49 have mammograms every 1.5 years.
Still, even with regular mammograms, many breast cancers aren’t detected until they’re larger than 2 cm (about the size of a peanut) in size. Breast cancers that are smaller than 2 cm are considered stage I cancer, and cancers that are larger than 2 cm are considered stage II cancers. So the researchers who did this study wanted to identify the risk factors linked to breast cancers not being found until they were larger than 2 cm. They also wanted to know if the cancer being larger at diagnosis affected the women’s long-term outcomes.
The researchers looked at the records of 2,358 women between the ages of 55 and 74 who were diagnosed with invasive breast cancer in Sweden from 2001 to 2008. They followed the women until 2016 and looked to see if the cancer’s size at diagnosis and prognosis was linked to BMI or breast density.
For breast cancers found by a screening test such as a mammogram, both higher BMI and higher breast density were linked to having a larger breast cancer at diagnosis.
For breast cancers found in the time between screening tests -- doctors call these interval cancers -- only a higher BMI was linked to having a larger breast cancer at diagnosis.
Among interval cancers, women with higher BMIs had a worse prognosis than women with lower BMIs. Breast density was not association with prognosis.
"Our study suggests that when a clinician presents the pros and cons of breast cancer screening to the patient, having high BMI should be an important 'pro' argument," said Fredrik Strand, M.D., radiologist at the Karolinska University Hospital in Stockholm, Sweden. "In addition, our findings suggest that women with high BMI should consider shorter time intervals between screenings."
Strand also said that women with higher BMIs may have other factors that may lead to a worse prognosis, including the molecular makeup of the cancer tumor and hormone receptor levels that make the cancers harder to treat.
At Breastcancer.org, we believe that a woman’s best chance for early detection requires coordination of our current screening tools:
- high-quality mammography
- clinical breast exam
- breast self-exam
To not use all three tools are missed opportunities for early detection.
The reality is that every woman is at risk for breast cancer, and this risk tends to increase over time. It’s important to understand and regularly update your health information related to breast cancer risk throughout your life with your doctor. To get the conversation started, here are some points to talk to your doctor about:
- family history of breast or other related cancers (ovarian, melanoma)
- any test results for abnormal genes linked to a high risk of breast cancer
- results of past breast biopsies, even if they were benign
- personal history of being treated with radiation to the face and/or chest before age 30
- breast density
- weight, if you’re overweight or obese
- level of physical activity
- any use of postmenopausal combined hormone replacement therapy (HRT)
- alcohol consumption, if you regularly drink more than 3 alcoholic beverages per week
- the amount of processed food and trans fats you eat
- your smoking history
- whether or not you had a full-term pregnancy or breastfed
If you have a higher-than-average risk for breast cancer because of any of the above factors, you might want to talk to your doctor about starting annual mammograms at a younger age and consider other screening tools (such as MRI or ultrasound) to maximize the opportunity for early detection.
For more information on mammograms, including where to get one and the benefits and risks, visit the Breastcancer.org Mammograms page.