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Adjunctive Ultrasonography Reduces Advanced Breast Cancer Incidence in Women Aged 40–49
Over a median follow-up exceeding 11 years, adding ultrasonography to mammography screening was associated with about a 17% lower risk of advanced breast cancer in women aged 40–49 compared with mammography alone (HR 0.83, 95.6% CI 0.70–0.98). The reduction was most pronounced between four and eight years after screening began, suggesting a meaningful but time-limited window of benefit.
What Was Studied
This analysis asked whether adjunctive ultrasonography screening—beyond standard mammography—could reduce the long-term cumulative incidence of advanced-stage breast cancer in younger women. Because younger women, particularly those with dense breast tissue, are less well served by mammography alone, quantifying the downstream impact on disease stage at detection is a critical evidence gap for screening policy.
How It Was Studied
This is a prespecified secondary analysis of the J-START randomised controlled trial, a large government-funded study conducted across 42 sites in 23 Japanese prefectures. Asymptomatic women aged 40–49 without prior breast or other cancers were enrolled between August 2007 and March 2011 and randomly assigned in a 1:1 ratio to receive either mammography plus ultrasonography or mammography alone, with two screening rounds over a two-year period. A total of 72,661 women were included—36,723 in the intervention arm and 35,938 in the control arm. The primary outcome for this analysis was the cumulative incidence of stage 2 or higher breast cancer (by TNM classification), with data tracked through October 2024, yielding a median follow-up of approximately 11.4 years in the intervention group and 11.3 years in the control group.
What Was Observed
- Fewer advanced cancers in the ultrasonography group: Of 894 breast cancers detected in the intervention group, 234 (26%) were classified as advanced stage, compared with 277 of 843 (33%) in the mammography-only group—a statistically significant difference representing roughly a 17% lower hazard of advanced cancer with adjunctive ultrasonography (HR 0.83, 95.6% CI 0.70–0.98; p=0.026).
- Benefit was not constant over time: Kaplan-Meier analysis indicated a violation of the proportional hazards assumption, meaning the risk reduction was not uniform throughout follow-up. The significant divergence in advanced cancer incidence occurred specifically between 48 and 96 months (years four through eight), with curves separating around year four and stabilising after year eight.
- Higher overall cancer detection in the intervention arm: The total number of breast cancers detected was modestly higher in the ultrasonography group (894 vs. 843), consistent with the known sensitivity advantage of combined imaging—but the proportion reaching advanced stage was meaningfully lower, suggesting earlier interception rather than mere overdetection.
Why This Matters
Demonstrating that a screening modality reduces advanced-stage incidence—not merely detection rates—provides stronger evidence that earlier detection translates into stage shift with potential survival implications. This is a long-standing evidentiary standard in screening research, and J-START now offers one of the few randomised datasets capable of addressing it. The findings carry particular relevance for Asian populations, in whom dense breast tissue is prevalent and mammographic sensitivity is correspondingly limited, potentially supporting reconsideration of screening protocols in these groups.
How to Read This Result
While the long follow-up and large sample size strengthen confidence in the direction of effect, the time-restricted nature of the benefit and the violation of the proportional hazards assumption introduce complexity that warrants careful interpretation before these findings are applied to other populations or screening systems.
Limitations
The abstract does not explicitly report study limitations.