Obesity May Explain Some Of The Breast Cancer Mortality Gap Between Black And White Women

Data from women with early breast cancer suggests the 40% mortality gap between Black and white women in the U.S. may be at least partly attributable to higher rates of obesity and obesity-related comorbidities among Black women, researchers say.

In a retrospective chart review that included 548 breast cancer patients, the study team found that 62% of Black women were obese as compared to 32% of white women. At diagnosis, 62% of Black women and 47% of white women had two or more obesity-related comorbidities. Most individual comorbidities were also more common in Black women than white women, including hypertension (60% vs 32%); diabetes (23% vs 6%); hypercholesterolemia or hyperlipidemia (28% vs 18%); and hypothyroidism (4% vs 18%), according to the results published in Cancer.

"Many women with early breast cancer are obese and that's not surprising because obesity is a risk factor for breast cancer," said the study's lead author, Kirsten Nyrop, an assistant professor in the division of oncology at the School of Medicine at the University of North Carolina, Chapel Hill. "But it's much higher in Black women."

Other studies have found a 40% mortality disparity between Black and white women with breast cancer, Nyrop said. "If you look at the disparity literature, researchers often look at financial disparities, differences in access to affordable healthcare, and things at the front end that delay timely treatment or getting mammograms," she added. "But once women are in the clinic, there is still this difference. Our estimate is that 20% of the disparity could be explained by obesity and comorbidities."

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To investigate the possibility that obesity might explain, at least in part, the mortality disparities between Black and white women with breast cancer, Nyrop and her colleagues focused on women aged 18 years or older with stage I to III breast cancer and for whom weight data was available for two years after primary treatment.

Of the study group, 144 (26%) were Black and 404 (74%) were white. Average age was 55 for Black women and 57 for white women; 65% of the Black women and 74% of the white women had HR+/HER2- tumors.

In addition to weight and related comorbidities, the researchers also investigated the possibility of treatment disparities, focusing on the patients with HR+/HER2- tumors because there can be some flexibility in treatment plans for these patients as compared with other breast cancers for which chemotherapy is the sole option.

While there were some differences by race - Black patients were younger, for example - there were no significant differences between Black and white women in the type of surgery (lumpectomy vs mastectomy), chemotherapy timing (neoadjuvant vs adjuvant) or type (anthracycline-based vs not anthracycline-based), receipt of radiation treatment, or endocrine treatment.

The findings suggest that oncologists should be having conversations with their obese patients after treatment has concluded about the impact of weight on cancer recurrence, Nyrop said. "If you can't talk with everybody who comes in, focus on those at greatest risk for weight gain," she said, adding that clinicians should consider referring patients to specialists for advice on nutrition and exercise.

Dr. Otis Brawley welcomed the new research.

"This is a really, really interesting paper," said Dr. Brawley, Bloomberg Distinguished Professor of Oncology and Epidemiology in the Johns Hopkins School of Medicine and the Johns Hopkins Bloomberg School of Public Health in Baltimore.

"While obesity is a huge problem in the U.S. as a whole, it is especially so for Black women," he added. "Many people have been looking at differences in Black and white patients and they frequently think that disparities in mortality are due to genetic, inherent and non-changeable influences."

But the new paper suggests that may be wrong, Dr. Brawley said. "It may just be this huge influence sitting right in front of us - that is changeable. We need to stop medicalizing race, stop assuming different races have different genetics and focus more on the societal aspects of race."

The most important part of the study is that it shows that a much higher proportion of Black women are obese and a very high proportion of them have comorbid diseases, Dr. Brawley said.

Consider the impact of insulin levels on cancer, Dr. Brawley said. "People who are overweight have a large amount of insulin in their blood," he added. "Insulin is a growth factor and in high amounts it stimulates the growth of blood vessels. A tumor needs blood vessels to get nourishment and to grow."

The take-home message from this study, Dr. Brawley said, "is that we need to pay a great deal more attention to energy imbalance. While the researchers use the term obesity, that's really the result of a lack of physical activity, a consumption of too many calories, and excess storage."

—Linda Carroll

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