Younger Survivors Have a Lower Risk of Secondary Primary Breast Cancer

Genetic testing may help both doctors and breast cancer survivors with decision-making and follow-up care.

Certain breast cancer survivors may have a lower risk of developing a secondary primary breast cancer (SPBC) within the first 10 years after diagnosis, a JAMA Network study noted.

Specifically, study researchers found that younger breast cancer survivors who do not have a germline pathogenic variant have a lower risk of having an SPBC after 10 years from diagnosis. Researchers noted that germline genetic testing may help doctors and survivors with decision-making and follow-up care options.

An SPBC is “a new breast cancer, distinct from the original, arising in either the ipsilateral or contralateral breast,” the researchers defined.

Risk Percentages for Secondary Primary Breast Cancers

The study included 685 women with stages 0 to 3 breast cancer who received unilateral mastectomies or lumpectomies as primary surgery. At breast cancer diagnosis, the average age was 36 years old. Most women had stage 1 or 2 primary breast cancer (79%), hormone receptor-positive tumors (77%) and HER2-negative tumors (69%).

At a median follow-up of 10 years, researchers found that 17 of 685 women developed an SPBC. Among these 17 women, two had disease on the original breast and 15 developed breast cancer in the opposite breast, the researchers noted.

Based on these results, they also determined that the median time from primary breast cancer diagnosis to an SPBC was 4.2 years. Of note, 94 women experienced distant recurrences and 45 experienced locoregional recurrences, the researchers stated.

“In this evaluation of 685 patients with breast cancer who were diagnosed at age 40 years or younger and had at least one intact breast after treatment, we observed a low 10-year risk of SPBC (2.2%) among noncarriers of pathogenic variants,” the researchers wrote.

According to the results of the study, women who were germline pathogenic variant carriers were at higher risk of SPBC. At five years, their risk was 5.5% higher and was 8.9% higher at 10 years, compared with noncarriers, researchers found.

“Among the subset of noncarriers of pathogenic variants, the association between in situ primary breast cancer and risk of SPBC was similar,” wrote the researchers.

The risk percentage was also higher among patients initially diagnosed with in situ breast cancer versus invasive breast cancer. At five years, patients with in situ and invasive breast cancers had a 6.2% and 1.2% risk, respectively, researchers noted. These risk percentages were at 10.4% versus 2.1%, respectively, at 10 years.

READ MORE: Differences Between Genetic, Genomic Testing in Breast Cancer

Importance of Genetic Testing for Breast Cancer

Regarding women who received bilateral mastectomies at or right after their primary diagnoses, four developed an SPBC, 43 developed local recurrences and five developed local recurrences.

The researchers established that women who underwent a bilateral mastectomy were “more likely to have been diagnosed with in situ disease [and] have a germline pathogenic variant,” they wrote.

“The results of this cohort study suggest a relatively low five- and 10-year cumulative incidence of SPBC among patients aged 40 years or younger with breast cancer who are noncarriers of PVs, emphasizing the importance of genetic testing among patients with breast cancer,” the researchers wrote.

An expert from the University of California San Francisco agreed that genetic testing is important for patients with breast cancer.

“All patients, in general, should be tested to see if they have [genetic] mutations, both for their family and then also importantly for themselves,” Dr. Laura Huppert said at the CURE® Educated Patient® Breast Cancer Summit.

Huppert is an assistant professor in the Division of Hematology/Oncology Department of Medicine at the University of California San Francisco.

During the summit, she emphasized that genetic testing is available for patients below the age of 65. However, a study from JAMA Network demonstrated that many patients still do not undergo genetic testing.

Particularly, the study evaluated more than 1 million patients diagnosed between 2013 and 2019 from California and Georgia. However, 26% of female patients and 50% of male patients with breast cancer reported undergoing genetic testing by March 2021.

“[It's] just really, really important to get germline genetic testing. And why is that? It's because we have better [treatment] options now,” Huppert said.

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