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The study found that while women diagnosed with HR-positive breast cancer have lower risk of progression to metastatic disease soon after the diagnosis, their risk persists for several years. In contrast, for women diagnosed with HR-negative disease, the risk of progression to metastatic disease is high soon after the diagnosis, but the long-term risk is lower than that for HR-positive disease.
Currently there are no reliable data on the risk of metastatic breast cancer recurrence after a non-metastatic breast cancer diagnosis, because registries do not routinely collect information on cancer progression or recurrence, Mariotto explained.
To estimate the risk of recurrence, Mariotto and colleagues used data from a cohort of 381,430 women, ages 15-84, diagnosed with breast cancer from 1992-2013, from the Surveillance, Epidemiology, and End Results Program (SEER) database.
The researchers applied a statistical technique called the “mixture-cure model” to the survival data to identify the “cure” fraction (fraction of women whose cancer did not progress). Then, they used two pieces of information that are available in the SEER database and published studies to estimate the time to metastasis for women in the “non-cured” fraction (fraction of women whose cancer progressed).
“For the mathematically minded, if we know that A=B+C, and if we know C and A, then we can estimate B,” explained Mariotto. “A is the time from diagnosis to death, B is the time from diagnosis to metastasis, and C is the time from metastasis to death. We estimated B using published studies on cohorts of patients diagnosed with recurrent metastatic breast cancer (A and C).”
“We were surprised by the insights the estimates provided into how the risk of recurrence for women diagnosed with early breast cancer in the United States varies with stage, HR status, age, year of diagnosis, and time since diagnosis,” Mariotto said. “We found that the risks of progressing to metastasis were lower for women diagnosed with breast cancer more recently, at younger ages, at early stage, and with HR-positive disease.”
Mariotto added that for women who survived five or more years after diagnosis, their chances of progressing to metastatic breast cancer within the next five years were lower if they were diagnosed with HR-negative breast cancer compared with women diagnosed with similar stage but with HR-positive breast cancer.
For example, among women diagnosed with stage 3 breast cancer at ages 60-74, the percent progressing to metastasis within five years from diagnosis is lower (34.5 percent) if their breast cancer is HR-positive and higher (48.5 percent) if their breast cancer is HR-negative. However, if they are still metastasis-free five years from diagnosis, the percent progressing to metastasis within the next five years is higher for HR-positive breast cancer (16.8 percent) versus HR-negative breast cancer (6.4 pe