Previous research has identified an increased risk of metastasis for women diagnosed with breast cancer within five years after giving birth. In a new study, however, researchers at the University of Colorado Cancer Center and Oregon Health & Science University have found that the higher metastasis risk for postpartum breast cancer (PPBC) lasts for 10 years after the last childbirth.
"This is the first study to demonstrate that a postpartum breast cancer diagnosed up to ten years after last childbirth can independently increase a woman's risk for developing metastasis to other parts of the body," commented Virginia Borges, MD, MMSc, Director of the Breast Cancer Research Program and Young Women's Breast Cancer Translational Program at the University of Colorado Cancer Center and co-senior author of the study, which was published in JAMA Network Open.
The study was conducted using data from the Colorado Young Women's Breast Cancer Cohort on 701 women aged 45 or younger with stage I to III invasive breast cancer. All patients' cancer was diagnosed between 1981 and 2014, and the average age at diagnosis was 37.9 years. The researchers found that breast cancer diagnoses within 10 years after a completed pregnancy were associated with increased risk of metastasis, particularly in women with stage I or II disease, whose risk was 3.5 to 5 times higher than those who had never given birth.
Furthermore, women diagnosed within 10 years after giving birth who had estrogen receptor (ER)-positive breast cancer—which generally has a better prognosis than ER-negative breast cancer—had a distant metastasis-free survival similar to that of patients with ER-negative cancer who had never given birth, with a 40% chance of metastasis after 15 years. The women diagnosed with ER-negative breast cancer within 10 years post partum were twice as likely to develop metastasis as women with ER-negative breast cancer who had never given birth.
Compared with other breast cancer patients, women with PPBC between five to 10 years post partum showed increased lymphovascular invasion—cancer's invasion to blood vessels and lymph channels—and women with PPBC less than five years after giving birth showed increased lymph node involvement at diagnosis.
"In these cancers, the tumors themselves do not appear different—there's no difference in the percent that are more aggressive subtypes, such as triple-negative or Her-2, no difference in the stage at which they are diagnosed, or other differences in classic measures that you might think would increase the chance of a bad prognosis," remarked Dr. Borges. "Instead, these data support previous findings from our team's lab work showing that after childbirth, conditions in surrounding breast tissue may aid the development of metastases. For example, we have shown that the laying down of new lymph channels in breast tissue after childbirth and nursing may allow cancer cells to better travel and seed sites of metastasis; sure enough, the current work finds more women having cancer in their lymph nodes at diagnosis."
Dr. Borges emphasized the importance of the study's results: "These findings highlight the need to understand that postpartum breast cancer may represent a unique subtype of cancer that requires distinct care. All women know when they last gave birth, so this is a readily available, free piece of information that helps us identify young women at highest risk from their breast cancer. If we are aware of the increased risk, we can work towards finding the best means to overcome this risk and treat it appropriately."
For More Information
Goddard ET, Bassale S, Schedin T, et al (2019). Association between postpartum breast cancer diagnosis and metastasis and the clinical features underlying risk. JAMA Netw Open, 2(1):e186997. DOI:10.1001/jamanetworkopen.2018.6997
Image credit: Sheheryar Kabraji and Sridhar Ramaswamy. Courtesy of the National Cancer Institute and Dana-Farber/Harvard Cancer Center at Massachusetts General Hospital