Black breast cancer patients are more likely to die than White patients, regardless of the type of cancer, according to a new study called Life After Cancer Epidemiology and Pathways.

These results suggest that the lower survival rate among Black patients is not solely because they are more often diagnosed with less treatable types of breast cancer, the researchers said.

For more than six years, the researchers followed nearly 1,700 breast cancer patients who had been treated for Luminal A, Luminal B, basal-like or HER2-enriched breast cancer subtypes. During that period, about 500 of the patients died, nearly 300 of them from breast cancer.

Blacks were nearly twice as likely as Whites to die. The researchers also found that Black patients were less likely than Whites to be diagnosed with either the Luminal A or Luminal B breast cancer subtypes.

“African Americans were more likely to have the hard-to-treat triple-negative breast cancer subtype and had a lower likelihood of having the Luminal A subtype, which tends to be the most treatable subtype of breast cancer and has the best prognosis,” said study author Candyce Kroenke, M.P.H., Sc.D., research scientist at Kaiser Permanente Division of Research in Oakland, Calif.

Kroenke and her colleagues found, however, that lower survival among Black patients was consistent across breast cancer subtypes. Black patients were 2.3 times more likely to die from the Luminal A breast cancer subtype compared with White patients; 2.6 times more likely to die from the Luminal B subtype; 1.3 times more likely to die from the basal-like subtype; and 2.4 times more likely to die from the HER2-enriched subtype.

“African Americans with breast cancer appeared to have a poorer prognosis regardless of subtype,” Kroenke said. “It seems from our data that the Black/White breast cancer survival difference cannot be explained entirely by variable breast cancer subtype diagnosis.”

Kroenke says there is very little research on risk factors and the less common subtypes, so consequently “we don’t really know” why African American women are frequently diagnosed with less treatable breast cancer subtypes. “In one study, Marilyn Kwan found that obesity was positively related to Triple Negative breast cancer. Obesity is more common in African American women and might have explanatory power,” continued the researcher.

Additionally, although Black women tend to be diagnosed at a later stage, Kroenke says while this challenge does account for some of the disparity, it does not to cover all of it.

Kroenke says there are many reasons why African American women have worse breast cancer mortality rates some known and others not: differences in co-morbity; aggressiveness of tumors, breast cancer subtype differences, potential treatment differences, etc.”

According to the Susan G. Komen for the Cure website, most breast cancers are Luminal A tumors. These cells look the most like the cells of breast cancers that start in the inner (luminal) cells lining the mammary duct.

Luminal B tumors have cells that look like those of breast cancers that start in the inner (luminal) cells lining the mammary ducts.

Women with Luminal B tumors are often diagnosed at a younger age than those with Luminal A tumors. And, compared to Luminal A tumors, they tend to have factors that lead to a poorer prognosis.

In some studies, women with Luminal B tumors have fairly high survival rates, although not as high as those with luminal A tumors.

Basal-like tumors have cells with features similar to those of the outer (basal) cells lining the mammary ducts. Most triple negative tumors are basal-like and most basal-like tumors are triple negative. However, not all triple negative tumors are basal-like and not all basal-like tumors are triple negative. About 15 to 20 percent of breast cancers are triple negative or basal-like. These tumors tend to occur more often in younger women and African Americans.

Triple negative/basal-like tumors are often aggressive and have a poorer prognosis (at least within the first five years after diagnosis) compared to the estrogen receptor-positive subtypes (luminal A and luminal B tumors).

HER2 type tumors are named for their HER2/neu-positive status. About 10 to 15 percent of breast cancers have this molecular profile and about 75 percent of HER2 type tumors contain p53 mutations.

HER2 type tumors have a fairly poor prognosis and are prone to early and frequent recurrence and metastases. Women with HER2 type tumors appear to be diagnosed at a younger age than those with luminal A and luminal B tumors.

HER2/neu-positive tumors can be treated with the drug trastuzumab (Herceptin).

Given all these factors Kroenke recommends, based on limited literature, that maintaining a healthy weight and diet could be important. She notes that the best science also supports obtaining mammogram screens after age 50 and repeating the test every two years.

On the other hand, the American Cancer Society and other organizations recommend that screenings begin at 40 and continue annually.

The Mayo Clinic supports screening beginning at age 40 and annually after that, because screening mammograms can detect breast abnormalities early in women in their 40s. Findings from a large study in Sweden of women in their 40s who underwent screening mammograms showed a decrease in breast cancer deaths by 29 percent.

But mammogram screening isn’t perfect, notes the Mayo Clinic website. Another study concluded that despite more women being diagnosed with early breast cancer due to mammogram screening, the number of women diagnosed with advanced breast cancer hasn’t decreased. The study suggested that some women with early breast cancer were diagnosed with cancer that may never have affected their health.

Unfortunately, doctors can’t distinguish dangerous breast cancers from those that are non-life-threatening, so annual mammograms remain the best option for detecting cancer early and reducing the risk of death from breast cancer, Mayo Clinic says.

The Life After Cancer study results were presented at the annual meeting of the American Association for Cancer Research, which took place April 6 to 10 in Washington, D.C. Data and conclusions presented at meetings typically are considered preliminary until published in a peer-reviewed medical journal.

Robert Preidt contributed to this story.