THURSDAY, May 18, 2017 (HealthDay News) -- The number of U.S. women living with the most advanced stage of breast cancer has been rising since the 1990s, a new study finds.
Researchers say that treatment advances, allowing more breast cancer patients to survive longer, are one likely reason. The general aging of the U.S. population is another.
Right now, the study estimated, close to 155,000 U.S. women are living with metastatic breast cancer -- cancer that has spread beyond the breast to distant sites in the body. That is up from roughly 105,000 in 1990.
Breast cancer experts said the figures are actually the first estimates of how many U.S. women are living with metastatic disease.
A number has been hard to come by, they said, because there is no national system that tracks cancer recurrences: Since U.S. women are typically diagnosed with earlier-stage breast cancer, most metastatic cases would -- presumably -- be in women who'd suffered a recurrence affecting distant sites in the body.
"That's what we've assumed," said Stephanie Reffey, senior director of evaluation and outcomes for Susan G. Komen, a nonprofit that supports breast cancer research.
Why is it important to have actual numbers, or at least reliable estimates?
For one, it can help drive more research, according to Reffey, who was not involved in the study.
By the researchers' estimates, three-quarters of all women with metastatic breast cancer were initially diagnosed with earlier-stage cancer.
"That's really important information," Reffey said. "We need more-focused research into preventing those recurrences."
Lead study author Angela Mariotto agreed.
The findings shine a light on a group of cancer patients who've "never been properly documented before," said Mariotto, a researcher with the U.S. National Cancer Institute.
The study did find some encouraging trends, she noted: Survival among women initially diagnosed with metastatic breast cancer is improving -- especially those diagnosed before age 65.
In the early 1990s, women diagnosed with metastatic breast cancer before age 50 typically lived for 22 months. By 2012, that had increased to about 39 months.
There was a similar pattern among women diagnosed between the ages of 50 and 64: Their typical survival rose from 19 months in the early 1990s to almost 30 months in 2012.
More women are also surviving for prolonged periods, the study found. Among women diagnosed before age 50, the five-year survival rate doubled between 1992 and 2012 -- from 18 percent to 36 percent.
Those figures come from a U.S. surveillance system that tracks new cancer diagnoses and deaths. It lacks information on women's survival after a breast cancer recurrence.
Mariotto could not say exactly why survival has improved.
But there were treatment advances during the study period, she noted: The drug Herceptin, for example, was approved in 1998 for treating some cases of metastatic breast cancer. It is one of a group of "targeted" drugs that zeroes in on specific abnormalities in cancer cells.
"We do have some evidence that progress is being made," Reffey said. But, she added, "these women are still not living long -- so it's not great news."
The hope, according to Reffey, is to help women with metastatic breast cancer not only live longer -- but also have a good quality of life.
"We'd like to see it become more of a livable, chronic disease," Reffey said.
Some women, she noted, do live for years with metastatic breast cancer. Of women younger than 65 in this study, 11 percent of those diagnosed between 2000 and 2004 were still alive a decade or more later.
Those women, Reffey said, show that long-term survival is possible.
The findings were published online May 18 in the journal Cancer Epidemiology, Biomarkers & Prevention.
Susan G. Komen has more on metastatic breast cancer.