A mysterious surge in incurable breast cancer among younger women has sparked alarm among experts.
A major US study found diagnoses of stage 4 breast cancer – when the disease has already spread around the body and can no longer be cured – climbed nearly 18 percent over the last decade.
The steepest increases were seen in women under 40, despite breast cancer traditionally being far more common in older patients.
Researchers were particularly concerned by a rapid rise in triple-negative tumours – one of the deadliest and hardest-to-treat forms of the disease, which kills nine in 10 patients once diagnosed at stage 4.
Scientists say they still do not know what is driving the trend. But changes in screening, obesity, women having children later in life and exposure to hormone-disrupting chemicals found in plastics have all been suggested as possible factors.
Breast cancer experts have urged more research into the causes of the rise, warning that much about the trend remains unknown.
‘In the United States today, there are 170,000 women… living with advanced breast cancer, and this number is expected to grow substantially over the next decade,’ warned Dr Lauren C Pinheiro, an internal medicine physician at Weill Cornell Medicine in New York who was not involved in the study.
‘The authors emphasize an urgency for the field to identify drivers of increased advanced-stage diagnoses, which should serve as a call for additional, population-health research on this growing patient population.’
Actor Olivia Munn was diagnosed with breast cancer at age 42 and underwent a double mastectomy
About 322,000 women in the US are diagnosed with breast cancer every year, according to the American Cancer Society, and around 42,000 die from the disease.
Roughly six percent of cases are diagnosed at stage 4, meaning the cancer has already spread to other parts of the body such as the bones, lungs, liver or brain.
The new study, published in JAMA Network Open, analyzed data from 761,471 breast cancer patients between 2010 and 2021. About 99 percent were women.
Of those patients, 43,934 – roughly five percent – had stage 4 cancer at the time of diagnosis.
The researchers found the rate of stage 4 breast cancer diagnoses increased from 9.5 cases per 100,000 women in 2010 to 11.2 per 100,000 in 2021 – an average annual rise of 1.2 percent.
But the increases were far sharper among younger women.
Patients under 40 saw diagnoses climb by 3.1 percent every year – nearly three times the overall rate.
The researchers also found triple-negative breast cancers rose by an average of 2.7 percent annually.
Sarah Citron, 33, was diagnosed with breast cancer after noticing a lump in her armpit. Doctors originally blamed the lump on hormonal changes from having her IUD removed to try for another child
Triple-negative breast cancer is considered particularly dangerous because the tumours do not respond to hormone-based therapies that are often highly effective in other breast cancer patients.
When diagnosed at stage 4, the disease kills around nine in 10 patients.
Though men account for only a small percentage of breast cancer cases, the study also found stage 4 diagnoses in men rose 3.7 percent annually between 2010 and 2021.
The rate increased from 0.12 per 100,000 men to 0.2 per 100,000 over the study period.
Overall, stage 4 diagnoses rose from 5.6 percent of all breast cancer cases in 2010 to six percent in 2021.
The researchers said several possible factors may be contributing to the increase.
One theory is that women having children later in life could raise the risk because pregnancy helps breast cells mature in a way that may make them less vulnerable to cancerous changes.
Rising obesity rates have also been linked to breast cancer risk because excess body fat can fuel inflammation and alter hormone levels.
Other research has pointed to endocrine-disrupting chemicals found in plastics and microplastics, which scientists fear may damage breast tissue over time.
Pinheiro also warned younger patients diagnosed with stage 4 breast cancer often face major financial, emotional and social pressures alongside the disease itself.
She said many must balance treatment with work and family responsibilities while also coping with mental health problems such as depression.
‘Taken together, these findings underscore a need not only to identify and understand drivers of incident de novo metastatic breast cancer but also to find ways to better support the multifaceted, complex needs of this growing patient population,’ she wrote.
‘We encourage oncology care teams to consider implementing routine screening of health-related social and supportive care needs for patients with metastatic breast cancer in clinical practice.’
