Rising Obesity and Declining Fertility Linked with Increasing Breast Cancer Cases in U.S.

A decades-long decline in breast cancer deaths in the U.S. has started to slow, while diagnosed cases of the condition have increased slightly—a trend that scientists believe could be partly caused by the obesity epidemic and declining fertility.

Breast cancer is the most common type of the disease in the U.S. other than skin cancers. It is the second most deadly form of the condition for women—with only lung cancer killing more.

The most common type of the disease in the U.S. apart from skin cancers, breast cancer is the deadliest form of the condition in women after lung cancer.

Between 2012 and 2016, the average incidence rate of breast cancer climbed by 0.3 percent per year, according to the study published in the journal CA: A Cancer Journal for Clinicians.

Figures collected by the National Cancer Institute's Surveillance, Epidemiology, and End Results program and the Centers for Disease Control and Prevention's National Program of Cancer Registries showed a 40 percent drop in breast cancer deaths between 1989 to 2017.

Researchers believe this amounts to 375,900 lives being saved. But from 1998 to 2011, the pace of decline slowed from a yearly decrease of 1.9 percent, dropping to 1.3 percent between 2011 and 2017.

The study also revealed that in the five years following 2013, the number of Hispanics dying of breast cancer dropped by 2.1 percent; by 1.5 percent in black women; 1 percent among whites; and 0.8 percent in Asians/Pacific Islanders. Rates remained the same for American Indians and Alaska Natives.

Yet despite a slightly lower incidence rate among black women, this group was found to be 40 percent more likely to die from breast cancer when compared with white women.

In a pattern that has emerged over the past three decades—and which stabilized in 2011—black women have the highest breast cancer death rate of any racial and or ethnic group in the U.S. The death rate among black women aged 50 and over is double that of white women.

The most recent data from 2016 to 2017 showed more black women died of breast cancer than lung cancer in six U.S. states: Arizona, Colorado, Florida, Georgia, Mississippi, and South Carolina. The same trend was found among white women in Utah.

Looking at the figures state by state, researchers found rates of breast cancer did not drop in Nebraksa between 2013 and 2017, bucking the nationwide trend. The same pattern was seen among black women in Colorado and Wisconsin; and white women in Nebraska, Texas, and Virginia.

When the numbers were crunched according to subtype, the team found rates of hormone receptor-positive (HR+) breast cancers are increasing in all groups, whereas hormone receptor-positive negative (HR-) breast cancers are decreasing.

The decline could pick up if patients are given access to high-quality prevention programs, if the disease is detected earlier, and all women can access treatment services, the researchers wrote.

Carol DeSantis, principal scientist in surveillance and health services research at the American Cancer Society (ACS), and lead author of the study, told Newsweek: "The increase in HR+ breast cancer rates are likely due in part to rising rates of obesity and declining fertility rates because obesity increases risk and having more children decreases risk of HR+ breast cancer.

"Much less is known about risk factors for HR- breast cancer, but having more children is associated with higher risk, so declining fertility rates may also be contributing to decreasing rates of this subtype."

DeSantis told Newsweek it is not clear what is causing the decline in breast cancer death rates to slow—but she said past studies suggest the steep drops were due to improvements in treatment, the disease being diagnosed earlier, and increase awareness.

"It may be that...most women are getting screened and many have access to high-quality breast cancer treatment," she said.

"Still, our data also show that disparities remain and not all women are getting diagnosed at early stages or have access to high-quality treatments. For example, screening rates are much lower for women who are uninsured. And black women remain 40 percent more likely to die from breast cancer compared to white women, despite having similar risk of diagnosis," she said.

"Increasing breast cancer incidence rates are likely due in part to the rising prevalence of obesity," she continued. Women can reduce their risk of developing the condition by maintaining a healthy body weight, being physically active, and drinking as little alcohol as possible.

"All of these factors are independently associated with breast cancer risk, which means exercise can lower your breast cancer risk even if you don't lose weight," she said.

"Regular mammography screening is the best way to diagnose breast cancer at the earliest possible stage, which is associated with the best outcomes. ACS recommends mammography screening for average risk women ages 45 and older."

Addressing why black women are, on average, more likely to die of breast cancer when compared with white women, DeSantis said there are many contributing factors—including that this demographic is more likely to be diagnosed with breast cancers that are more advanced or later stage at diagnosis, and with the subtype known as triple negative breast cancer. This is where the tumour does not contain three receptors which usually fuel growth, meaning treatments like hormone therapy are not available.

"Access to high quality treatment, which is limited by insurance and other socioeconomic factors, contributes to these inequitable breast cancer outcomes," she said. "The prevalence of obesity is also higher in black women, which is associated with poorer survival in breast cancer patients."

According to research published earlier this year, an estimated 268,600 new cases of breast cancer will be diagnosed among women in the U.S. in 2019, with some 41,760 women dying from the disease.

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Research has revealed a decades-long drop in breast cancer death rate has continued. In this stock image, a doctor holds a mammogram in front of x-ray illuminator. Getty