Paradox of engagement: precautionary public health alerts and gender inequality in cancer diagnosis—a quasi-experimental study

BACKGROUND: Emergency policies designed to protect populations can inadvertently cause diagnostic harm when essential services are suspended. How such policies reshape gender gaps in cancer detection, and whether either sex faces disproportionate harm, remains underexplored. OBJECTIVES: We leveraged Taiwan's 2021 level 3 alert-a precautionary directive implemented during minimal COVID-19 transmission (0.07%) that mandated hospital capacity reductions and school closures-as a natural experiment to test whether the alert produced gendered diagnostic disruptions. METHODS: Using Taiwan Cancer Registry and National Health Insurance claims (N=312 522; 2015-2021), we employed interrupted time series and difference-in-differences models to estimate changes in cancer detection rates and tumour size at diagnosis; robustness was confirmed through sensitivity and falsification tests. RESULTS: The alert disproportionately reduced detection of early-stage cancers, consistent with a collapse of preventive and opportunistic detection pathways. Women experienced larger declines in detection than men (-43.9% vs -32.0%; p=0.001) and greater increases in tumour size (17.3% vs 11.5%; p=0.026). These gaps were most pronounced among women under 50 (-50.7% vs -25.5%; p=0.001) and disadvantaged women, whose tumour size increase was nearly double that of disadvantaged men (16.6% vs 8.8%; p=0.049). The gap was particularly large for opportunistically detected cancers (lung: -47.1% women vs -22.6% men; p=0.011). CONCLUSIONS: These findings reveal a system-level patient safety failure. Women's higher engagement with routine care, ordinarily a health advantage, became a structural vulnerability when these pathways were suspended, possibly amplified by intensified caregiving, employment shocks and infection-risk avoidance. As health systems prepare for recurring shocks, resilience planning must incorporate gender-sensitive safeguards that prevent diagnostic harm. Protecting early detection pathways is both a clinical imperative and a patient safety requirement for equitable emergency response.