The data come from a massive meta-analysis of more than 400 studies conducted around the world, involving tens of thousands of women.
It found that the overall risk of metastasis is between 6% and 22%, with younger women having a higher risk.
While women aged 50 years or older when they were diagnosed with breast cancer have a risk of developing metastasis that ranged from 3.7% to 28.6%, women diagnosed with breast cancer before age 35 had a higher risk – 12.7% to 38%. The investigators speculate that this may be because younger women have a more aggressive form of breast cancer or because they are diagnosed at a later stage.
The risk of metastasis also varies by tumor type, with luminal B cancers having a 4.2% to 35.5% risk of metastasis versus a 2.3% to 11.8% risk with luminal A tumors.
“The quantification of recurrence and disease progression is important to assess the effectiveness of treatment, evaluate prognosis, and allocate resources,” commented lead investigator Eileen Morgan, PhD, of the International Agency for Research on Cancer.
Dr. Morgan and colleagues presented the new meta-analysis at the virtual Advanced Breast Cancer Sixth International Consensus Conference.
She added that this information has not been available until now “because cancer registries have not been routinely collecting this data.”
In fact, the U.S. National Cancer Institute began a project earlier this year to track this information, after 48 years of not doing so.
Reacting to the findings, Shani Paluch-Shimon, MBBS, director of the Breast Unit at Hadassah University Hospital, Jerusalem, commented that this work “provides the first reliable estimate of how many breast cancer patients go on to develop advanced disease in contemporary cohorts.”
“This information is, of course, important for patients who want to understand their prognosis,” she continued.
“But it’s also vital at a public health level for those of us working to treat and prevent advanced breast cancer, to help us understand the scale of the disease around the world,” she said. “It will help us identify at-risk groups across different populations and demonstrate how disease course is changing with contemporary treatments.”
“It will also help us understand what resources are needed and where, to ensure we can collect and analyze quality data in real-time as this is key for resource allocation and planning future studies.”
The work was funded by a grant from the Susan G. Komen Foundation.
A version of this article first appeared on Medscape.com.