A concerning increase in incurable breast cancer among younger women has alarmed researchers. A major US study revealed that diagnoses of stage 4 breast cancer—when the disease has already spread and cannot be cured—rose by nearly 18 percent over the past decade.
Steepest Increases in Women Under 40
The most significant rises were observed in women under 40, despite breast cancer traditionally being more common in older patients. Researchers were particularly troubled by a rapid increase in triple-negative tumours, one of the deadliest and hardest-to-treat forms, which kills nine in ten patients once diagnosed at stage 4.
Scientists remain uncertain about the cause of this trend. Potential factors include changes in screening practices, rising obesity rates, women having children later in life, and exposure to hormone-disrupting chemicals found in plastics.
Call for More Research
Breast cancer experts have urged further investigation into the drivers of this rise. Dr Lauren C Pinheiro, an internal medicine physician at Weill Cornell Medicine in New York, who was not involved in the study, stated: '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. The authors emphasise 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.'
Approximately 322,000 women in the US are diagnosed with breast cancer annually, according to the American Cancer Society, with around 42,000 deaths each year. Roughly six percent of cases are diagnosed at stage 4, meaning the cancer has spread to other parts of the body such as the bones, lungs, liver, or brain.
Study Details
The study, published in JAMA Network Open, analysed data from 761,471 breast cancer patients between 2010 and 2021, of whom about 99 percent were women. Of these, 43,934—roughly five percent—had stage 4 cancer at diagnosis. The rate of stage 4 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.
However, the increase was far sharper among younger women. Patients under 40 saw diagnoses climb by 3.1 percent annually—nearly three times the overall rate. Triple-negative breast cancers rose by an average of 2.7 percent per year. This form of cancer is particularly dangerous because tumours do not respond to hormone-based therapies effective for other breast cancers. When diagnosed at stage 4, it kills around nine in ten patients.
Although men account for only a small percentage of breast cancer cases, the study also found that stage 4 diagnoses in men rose 3.7 percent annually between 2010 and 2021, from 0.12 per 100,000 men to 0.2 per 100,000.
Possible Contributing Factors
Researchers suggest several factors may be contributing to the increase. One theory is that women having children later in life could raise risk because pregnancy helps breast cells mature, potentially making them less vulnerable to cancerous changes. Rising obesity rates have also been linked to breast cancer risk, as excess body fat can fuel inflammation and alter hormone levels. Other research points to endocrine-disrupting chemicals found in plastics and microplastics, which may damage breast tissue over time.
Dr Pinheiro also warned that younger patients diagnosed with stage 4 breast cancer often face significant financial, emotional, and social pressures. Many must balance treatment with work and family responsibilities while coping with mental health issues 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.'
