A statistical method could fill the gaps in the US cancer registry data to estimate the short- and long-term risk of recurrence of hormone receptor (HR) -positive and HR-negative breast cancers. 

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 after the diagnosis, but the long-term risk is lower than that for HR-positive disease. The study is published in the journal Cancer Epidemiology, Biomarkers & Prevention

"Progression to  metastatic breast cancer  is probably the most important concern women have when they are diagnosed with early-stage breast cancer," said Mariotto. "Knowing the risks of progressing to metastatic breast cancer is important for patients making decisions about their treatment as well as for cancer control experts identifying research priorities and health services planning."

Cancer progression or recurrence

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 were used 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).

HR-positive disease

"We were surprised by the insights provided by the risk of recurrence for women, diagnosed with early breast cancer in the United States, various status, 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."early stage, and with HR-positive disease."

Mariotto added that for those 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 cancersimilar stage but with HR-positive breast cancer.

"These are the first population-based estimates on the probabilities of progressing to metastatic disease for women, diagnosed with early-stage breast cancer in the United States," Mariotto noted. "The approach is applicable to other cancers and can improve our understanding of the burden of cancer in the population."

A limitation of the study is that the recurrence risk measures were developed by removing the chances of dying from other causes. "While these types of measures are useful for comparisons across groups of patients and for isolating the effect of a cancer diagnosis on survival, they may be less useful in predicting chances of recurrence at the individual level, especially for patients with comorbidities," Mariotto said .