Breast cancer is the most diagnosed cancer among women globally, and the number of cases worldwide is estimated to reach over 3.5 million by 2050, new research has found.

In high-income countries, decades of investment in screening, early detection and treatment drove a nearly 30% decline in breast cancer mortality between 1990 and 2023. But in the world’s lowest-income countries, the trend is moving in the opposite direction: Deaths from breast cancer have nearly doubled over the same period, according to a study published Monday in the journal The Lancet Oncology.

The findings, drawn from an analysis of breast cancer trends across 204 countries and territories for over three decades, show a deepening global divide between who lives and who dies from the most common cancer among women worldwide.

“There were improvements in mortality rates over time in higher-income settings, but there were really inequities in progress and increasing mortality in some lower-income settings,” said senior study author Dr. Lisa Force, an assistant professor at the University of Washington School of Medicine’s Institute for Health Metrics and Evaluation.

An estimated 2.3 million women were diagnosed with breast cancer globally in 2023, resulting in 764,000 deaths, according to the study. Nearly 1 in 4 cancers diagnosed in women worldwide that year was breast cancer.

While the death rate, adjusted to account for differences in population age across countries, dropped by nearly 30% in high-income nations between 1990 and 2023, it increased by roughly 99% in low-income countries over the same period. Meanwhile, the diagnosis rate in low-income countries rose by 147% over the same period.

For women living in sub-Saharan Africa, which includes some of the highest mortality rates worldwide, the numbers are especially alarming. Mortality rates in central and western sub-Saharan Africa are now more than double the global average, with roughly 35 deaths for every 100,000 people each year after adjusting for age.

“People’s outcomes from cancer depend on what country they live in,” said Dr. Kamal Menghrajani, an oncologist at Massachusetts General Hospital who wasn’t involved in the study. “And that shouldn’t be the case.”

A gap in infrastructure

The divergence reflects a fundamental mismatch between rising diagnosis rates and the infrastructure needed to treat the disease, Menghrajani explained.

Cancer awareness and screening are not enough, said Menghrajani, former assistant director for cancer innovation and public health in the Biden administration. “We need to have strong infrastructure in place to be able to treat people who have cancer and support them all the way through so that they can be cured.”

Treating breast cancer requires a carefully coordinated system, she said: surgery, radiation therapy, and chemotherapy or targeted treatments. In the United States, all three are generally available and covered by insurance.

In much of sub-Saharan Africa, the picture is dramatically different. As of 2020, only about half of African countries had any external beam radiotherapy service — the most common form of radiation therapy for breast cancer — and none had sufficient capacity to meet their populations’ needs, according to the study.

Where radiation is unavailable, mastectomy often becomes the default treatment, the study noted, but without the surrounding infrastructure of postoperative care and systemic therapy, even surgery has limited effectiveness.

The cost of some treatments compounds the problem. The authors wrote that a standard course of trastuzumab, a targeted therapy for a common subtype of breast cancer, combined with chemotherapy, can cost the equivalent of a decade’s average income in some lower-income countries.

“In low-income countries, people are being left behind,” Menghrajani said. “They’re finding cancer more frequently, and when they find it, they may not have the resources to offer the best treatment.”

Addressing the disparity will require “both political will and investment in strategies that really target the entire cancer care continuum,” Force said. She added that services need to be both accessible and affordable, and strategies should be integrated with broader noncommunicable disease efforts.

Force noted that the World Health Organization’s Global Breast Cancer Initiative recommends three pillars to reduce mortality: ensuring cancers are identified early, ensuring timely diagnosis after symptoms are noticed, and ensuring patients have access to comprehensive management.

“The most effective interventions are really going to include all of those things,” she said.

Without a meaningful approach, the study’s authors warn that many countries will fall short of the WHO’s Global Breast Cancer Initiative target of achieving a 2.5% annual reduction in mortality worldwide.

However, the study noted that even in the US, Black women have a death rate from breast cancer that is 40% higher than that of White women, a disparity that persists despite the country’s world-class treatment infrastructure.

“Even here in our own country, we have a lot of work to do to try to make sure that we have equitable care for cancer, no matter somebody’s socioeconomic, racial or other background,” Menghrajani said.

Force said the reasons are complex with multiple factors and mirrored patterns seen across countries: potentially more delayed diagnoses, treatment access gaps and biases in the care patients receive.

“Disparities within countries are sometimes similar to disparities between countries,” she said. “If you’re diagnosed later with breast cancer, the outcomes are generally poor.”

What you can do about breast cancer risk

While the study is primarily a call to action for global health change, it also offers guidance for individuals aiming to reduce their risk of breast cancer.

The most effective lifestyle adjustment is to limit consumption of red meat, followed by quitting tobacco use, managing your blood sugar, maintaining a healthy weight, curtailing alcohol use and staying physically active.

However, “lifestyle changes can’t fully eliminate the risk of breast cancer,” Menghrajani said. Force added that the majority of breast cancer causes are not attributable to lifestyle at all.

The US Preventive Services Task Force currently recommends women get a mammogram every other year starting at age 40 and continuing through age 74. Force said that anyone who is concerned about breast cancer or is in a higher-risk category, such as having a family history of breast cancer or obesity, should speak with a primary care provider if they have access to one.

Self-exams, once widely recommended, are no longer part of standard guidelines, Menghrajani said.

“Because so many women will end up finding changes in their breasts that are just related to their menstrual cycle that are not concerning for breast cancer, it’s no longer recommended to do monthly breast self-exams at home,” she said.

However, women should pay close attention to any new lump or mass they can feel in the breast, Force said, as well as subtler changes to the skin on the breast, the nipple or the overall shape.

“I would suggest that women really know their bodies and know if something’s different,” she said, “and feel empowered to advocate for themselves to get assessed appropriately.”

Not every change will be a sign of cancer, she noted, but any unexplained difference warrants a conversation with a medical provider.

“For the majority of women who are diagnosed with breast cancer in the US, it is diagnosed on mammography,” Menghrajani said. “Staying up with screening is really the best thing that people can do.”