Breast cancer is the most diagnosed cancer among U.S. women and the second leading cause of cancer death.

Black women who develop breast cancer are around 40% more likely to die of the disease than white women, but it was unclear until now whether this disparity exists across all types of breast cancer.

Now, a meta-analysis led by Mass General Brigham researchers shows that Black women have a higher risk of dying from breast cancer for all tumour subtypes, and the size of this disparity varies from 17-50% depending on the type of breast cancer.

These findings, published in the Journal of Clinical Oncology, demonstrate that higher mortality rates among Black women with breast cancer are at least partially attributable to factors that are independent of tumour biology—for example, socioeconomic inequality, delays in diagnosis, and inadequate access to timely quality cancer treatment resulting from systemic racism.

“Our findings demonstrate that multiple, interacting factors contribute to disparities in breast cancer survival between Black and white women,” said senior author Erica Warner, ScD, MPH, a cancer epidemiologist at Massachusetts General Hospital, a founding member of the Mass General Brigham healthcare system.

“To achieve equity, intervention is necessary at multiple levels—from community to healthcare systems and individual healthcare providers, to patients themselves learning about their disease and what their expectations should be for their care.”

Though it is often discussed as a single disease, breast cancer has multiple subtypes that differ in risk factors, treatment, and prognosis.

These subtypes are defined based on whether the cancer cells carry hormone receptors for estrogen or progesterone, which can be targeted for treatment, and whether they carry HER2 (human epidermal growth receptor 2), a protein associated with cancer aggressiveness and another potential treatment target. 

“There had been an anecdotal sense in the research community that differences in survival between Black and white women were greater for the most treatable forms of the disease—tumours that carry hormone receptors—and smaller for the historically less-treatable, hormone-negative tumours,” said Warner.

To investigate whether these anecdotes were supported by the evidence, Warner’s team combined data from 18 studies that were published between 2009 and 2022.

Altogether, these studies analysed 228,885 breast cancer cases, 34,262 of which were in Black women.

They found that survival was worse for Black women for all breast cancer subtypes, though the size of these disparities varied between breast cancer subtypes. There was a larger racial disparity for hormone-positive tumours, which were associated with a 34-50% higher risk of death for Black women, compared to hormone-negative tumours, which were associated with a 17-20% higher risk of death for Black women.

“These findings underscore a stark reality in our healthcare system: Black women are facing higher risks of death from breast cancer compared to their white counterparts, across all types of the disease. This disparity isn't just about biology,” said co-author Paulette Chandler, MD, MPH, associate epidemiologist in the Division of Preventive Medicine at Brigham and Women’s Hospital, a founding member of the Mass General Brigham healthcare system.

“It's a call to action for healthcare providers, policymakers, and communities alike to confront these inequities head-on and strive for meaningful change in breast cancer outcomes.”

Because hormone-negative tumours are less common, Warner says that racial disparities in breast cancer survival for hormone-negative subtypes were likely not observed previously because individual studies lacked statistical power due to the small number of cases.

“There may also be differences in the biological characteristics of some tumour subtypes between racial groups that our therapies are not attuned to, potentially because of underrepresentation of Black women in clinical trials,” said Warner.

However, these racial disparities are not inevitable, and the researchers point to several existing multilevel intervention programs that have successfully reduced disparities in cancer survival.

These programs leverage multiple strategies, including helping patients navigate the healthcare system, proactively identifying social needs and connecting patients with resources to address those needs, and by implementing systems that alert healthcare workers of missed appointments or unmet care milestones.

At the national level, interventions like ACCURE and Equal Hope aim to close gaps in mortality and survival between Black and white women.

Locally, MGH is collaborating with Boston Medical Center on a virtual Equity Hub for Cancer Treatment with the goal of enhancing partnerships and improving cancer care for underserved patients at community-based mental health centers.

Source: Mass General Brigham