Background

Breast cancer is a leading cause of death among women worldwide. Detecting cancer at an early stage is crucial for significantly improving survival rates. However, Asian women often have a higher prevalence of dense breast tissue, which limits the effectiveness of conventional screening methods. Standard diagnostic mammography struggles to detect tumors due to its inability to penetrate dense breast tissue. The medical community has therefore focused on adjunctive ultrasonography as a complementary approach to address these limitations. To evaluate the clinical effectiveness of this strategy, Japanese researchers initiated the large-scale randomized controlled trial J-START. In 2016, they reported an initial analysis showing that adding ultrasound to mammography could improve screening sensitivity, but this also increased the false positive rate, leaving the question of real survival benefits unresolved.

Key Findings

The latest secondary analysis, published in The Lancet, demonstrates the long-term effectiveness of this combined screening approach. Narumi Harada-Shoji, a doctoral researcher at Tohoku University Graduate School of Medicine, and her team randomly assigned 72,661 women in their 40s to either an intervention group (36,723 women) receiving both mammography and ultrasound or a control group (35,938 women) receiving mammography alone. The study followed participants for a median of 11.4 years. A total of 894 breast cancers were detected in the intervention group and 843 in the control group. When comparing the proportion of advanced breast cancers (stage 2 or higher), a clear difference was observed between the two groups. The intervention group had 234 cases of advanced breast cancer, accounting for 26 percent of all detected cancers, while the control group had 277 cases, representing 33 percent of all detected cancers. The hazard ratio (HR) for the cumulative incidence of advanced breast cancer in the intervention group was 0.83, 17 percent lower than in the control group (95.6% confidence interval [CI] 0.70–0.98, p=0.026). The difference in cumulative incidence rates became significant four years after the start of screening and reached its maximum at the eighth year before stabilizing.

Significance and Outlook

This study is considered a landmark in demonstrating that adjunctive ultrasonography not only detects more breast cancers but also reduces the actual incidence of advanced breast cancers with poor prognoses. It provides meaningful evidence for shaping national cancer screening policies in Asian countries, such as South Korea and Japan, where a relatively high proportion of women have dense breast tissue. However, concerns remain about whether the results from this clinical trial can be directly applied to large-scale national screening programs. Ultrasound interpretation is highly dependent on the skill of the operator, and untrained personnel conducting large-scale screenings may lead to increased diagnostic errors, unnecessary biopsies, and re-examinations, which can heighten patient anxiety and increase healthcare costs. Additionally, the difficulty in rapidly securing a sufficient number of trained medical professionals to meet nationwide screening demands is another challenge. Ultimately, for adjunctive ultrasound screening to deliver real benefits, it is essential to establish standardized guidelines to ensure consistent quality of the examinations.