Researchers at the National Cancer Institute and Fred Hutchinson Cancer Research Center have used a “mathematical recipe” to solve a longstanding puzzle: How many women in the U.S. are currently living with metastatic breast cancer (MBC).
Published this week in the journal Cancer, Epidemiology, Biomarkers & Prevention, the study estimates that as of January 2017 there are nearly 155,000 women living with the disease in the U.S., a quarter of whom were diagnosed from the very start with advanced cancer — known as de novo — and three quarters who progressed to MBC from early stage disease.
This is the first time the number of women living with MBC has been estimated, and it is part of an ongoing effort by the NCI to provide data on what it calls an “understudied population.”
All told, 3.5 million U.S. women have a history of breast cancer — from those who were just diagnosed, to those who’ve gone through treatment for early stage disease, to those who were initially or eventually diagnosed with MBC.
Metastatic breast cancer, or cancer that’s spread to other parts of the body, is still incurable. But the study found women are living longer with the disease and younger women diagnosed with MBC de novo are surviving twice as long as in years past. This group’s five-year survival rate doubled, from 18 percent from 1992–1994 to 36 percent from 2005–2012, most likely due to improvements in treatment.
This translates into “an increase of approximately one-third in the number of women living with MBC,” the authors wrote. Part of that increase is related to the aging of the U.S. population.
Fred Hutch biostatistician Dr. Ruth Etzioni, co-author of the study, said the new research reveals the “magnitude of the MBC problem,” which has been difficult to measure due to gaps in cancer databases, namely the Surveillance, Epidemiology, and End Results Program, known as SEER.
The registries, created and maintained by the NCI, are a “national treasure,” according to Etzioni. An ever-unfolding flower of data, SEER provides us with critical cancer statistics: who gets it, where they live, what kind of cancer they get, the stage and morphology of their tumor, the first course of treatment and, finally, whether the cancer kills them or not.
But like most of us, the set of registries has issues.
The biggest one, according to many patient advocates, is that it does not collect recurrence rates; if a person’s cancer comes back, the SEER registries don’t fold that information into the mix. Doing that would be “very resource intensive,” Etzioni said, because you’d have to be “continually checking on people to see if they’ve had a recurrence” which she said, is “not feasible at this point on a national scale.”
This lack of data makes it difficult to accurately assess how many people are actually living with terminal cancer. But there are creative workarounds, which is how Etzioni and lead author Dr. Angela Mariotto of the NCI attained their MBC estimates.
“It’s important to have more accurate estimates,” said Mariotto, who for the last 17 years has squeezed the SEER registries for every last ounce of useful data.
Mariotto said the MBC study is all part of a larger effort to beef up SEER, led by Dr. Lynne Penberthy, associate director for the Surveillance Research Program, within the NCI’s Division of Cancer Control and Population Sciences. Penberthy is also one of the authors of the new study, along with Dr. Marc Hurlbert of the Breast Cancer Research Foundation and Musa Mayer of the Metastatic Breast Cancer Alliance.
"We're trying to capture more data items and give a more complete picture of cancer treatment and cancer care," Mariotto said. "For example, we capture information on treatment, but we don’t have information on the agents for chemotherapy.”
The NCI is also crowdsourcing ideas to fill in SEER's data holes and enhance it. Folding in recurrence data is a top priority, Mariotto said, pointing to methods that might be used to flag recurrence in the future such as algorithms that use insurance claims data, pathology reports, lab tests and imaging results to point to cancer’s return.
For now, though, the NCI is relying on statistical modeling to estimate just how many women are living with the disease.
To do that Mariotto and Etzioni tapped the SEER registries for the number of women who’d received a de novo MBC diagnosis and the number of women who’d died of metastatic breast cancer.
Then they used “common sense and a mathematical recipe,” Etzioni said. First, they started with the numbers they had from a variety of sources:
To come up with numbers on incidence of MBC, including women who progressed from early stage breast cancer, the researchers used a back-calculation method previously used in Australia to reconstruct prevalence of recurrent cancer. The method has also been used in the U.S. to estimate prevalence of breast cancer survivors in certain states.
“It’s like you have A + B = C and you know C and B, so you can get A,” Etzioni explained. “This is an indirect way to learn about the number of women who are living with metastatic breast cancer. And that number has gone up. And the reason it’s gone up is that the survival for metastatic breast cancer has gone up. They’re living with it longer.”
Seventeen percent, or 26,455 women, in fact, had been living with an MBC diagnosis for 10 or more years and 16.5 percent, or 25,502 women, had been metastatic five to 10 years.
“One-third of women with metastatic cancer have been living with it for at least five years,” said Etzioni.
All in all, the number of women living with metastatic breast cancer increased 4 percent from 1990 to 2000 and 17 percent from 2000 to 2010. And the number is projected to increase by 31 percent from 2010 to 2020.
“At one time, a diagnosis of distant recurrence or de novo stage IV meant that death from breast cancer was likely to be imminent,” the authors wrote. “Today, with the development of new therapies … MBC is not the immediate death sentence it once was.”
But, they added, given the “growing burden of MBC, it is critical to collect data on recurrence to foster more research into the specific needs of this understudied population.”
Toward that end, Mariotto and Etzioni will be providing estimates on the risk of recurrence in a follow-up paper.
Patient advocate Beth Caldwell, 40, was diagnosed with MBC de novo three years ago and has been pressing for better data on metastatic patients ever since. She said the new MBC study was “a start” but she’d like to see much more done to fill in data gaps for all stage 4 patients.
“The idea that we don’t know how many people are living with a particular disease in this country seems pretty backward,” she said. “Especially in an era where Amazon can predict that I’m going to like a particular cell phone case.”
Knowing how many people are living with a terminal illness is crucial, she said, because then you know the amount of resources to put toward it.
“If most cancer deaths are caused by mets, we should be putting a lot more of our resources, our money, into metastatic research,” said the former civil rights lawyer and co-founder of the nonprofit metastatic patient group MetUp.
Caldwell also had questions about the mortality data gleaned from the National Center for Health Statistics.
“I personally know of a good friend who died of MBC but her death certificate said it was natural causes,” she said. “Modeling based on death data only gets us so far. Having an item in the SEER data registry that tracks when a cancer recurs metastatically could really help us understand the extent of the disease.”
Bridgette Hempstead, founder of the Seattle-area African American cancer support group Cierra Sisters and an MBC patient herself, said she wasn’t surprised at the news that metastatic patients were living longer but said more research was clearly needed.
“When I went back to Washington, D.C., to talk to our senator, I met a metastatic breast cancer patient who had been in treatment for 18 years,” she said. “Of course, they’re living longer. But when it comes to metastatic disease in people of color, you have a greater disparity. A lot of these women are diagnosed at a later stage or as metastatic from the onset. Why are they progressing? Why are doctors missing this? This data is very important. Too many doctors give up on patients who are metastatic.”
Both patients said they would love to work with researchers to enhance existing cancer databases. SEER and its data gaps, in fact, will be “one of the top discussions” at the 2017 Northwest Metastatic Breast Cancer Conference, which Caldwell is helping to organize.
What does she think of the research?
“It’s better to have some data than no data,” she said. “I’m glad they’re coming up with ways to get around [this].”
“This is a real step forward,” she said. “We’ve had the data from SEER for some time, but we needed to be more creative and squeeze more out of it.”
Diane Mapes is a staff writer at Fred Hutchinson Cancer Research Center. She has written extensively about health issues for NBC News, TODAY, CNN, MSN, Seattle Magazine and other publications. A breast cancer survivor, she blogs at doublewhammied.com and tweets @double_whammied. Email her at email@example.com. Just diagnosed and need information and resources? Check out our patient treatment and support page.