Current guidelines used by general practitioners to assess breast cancer risk in women under 50 significantly underestimate the number of cases, missing approximately 95 percent of those who eventually develop the disease, according to new research from the University of Cambridge.

The study examined data from 1,258 women under 50 as part of the Breast Cancer Now Generations study, which collected information between 2004 and 2011. Researchers found that relying solely on family history to determine high risk fails to identify the majority of women who go on to develop breast cancer within ten years.

At present, women under 50 with a strong family history of breast cancer are eligible for referral to specialist services, where they may undergo genetic testing and receive regular screening aimed at early cancer detection. However, the Cambridge research suggests that family history accounts for only 5 to 15 percent of breast cancer cases, leaving many at risk unflagged under the current system.

The study introduced a new risk assessment model incorporating multiple factors, including family history, reproductive history, lifestyle variables, and genetic information. This multifactorial approach identified roughly eight times as many women who developed breast cancer compared to the existing criteria. Applying these alternative guidelines would classify about 26.5 percent of women under 50 as higher risk and eligible for further evaluation, a substantial increase from the current rate of 1.4 percent.

Researchers argue that better early identification of high-risk individuals could improve treatment outcomes for breast cancer, which remains a leading cause of death among younger women. Dr. Juliet Usher-Smith, from the University of Cambridge’s department of public health and primary care, emphasized the need for enhanced screening methods to enable earlier intervention.

Breast Cancer Now, which supported the study, highlighted the limitations of the National Institute for Health and Care Excellence’s (NICE) current referral guidelines. Simon Vincent, the organisation’s chief scientific officer, stated that new approaches to risk assessment could aid in preventing some breast cancers or detecting them at a more treatable stage. He urged that these findings be carefully considered in the ongoing review of NICE’s family history guidelines.

In response, NICE acknowledged the study’s potential to improve risk identification through multifactorial models but maintained that current evidence does not yet justify changing existing familial breast cancer guidelines. The organisation said it welcomes further research and continues to monitor developments in this area.