A screening programme for breast cancer by mammography in a community shows a 30% reduction in breast cancer mortality among screened women compared to unscreened controls. A public health expert warns that this benefit may be overestimated due to 'lead-time bias.' Lead-time bias in screening means:

• A Survival appears longer from diagnosis because detection is earlier, even if actual date of death is unchanged ✓
• B Slow-growing tumors are preferentially detected by screening, inflating apparent survival
• C Participants who volunteer for screening are healthier than those who do not
• D Repeated screening detects regressing lesions that would never have caused symptoms

Explanation

Lead-time bias occurs because screening advances the time of diagnosis without necessarily extending actual survival. Measured from diagnosis, screened patients appear to live longer, but death still occurs at the same time as it would have without screening. To avoid lead-time bias, outcomes should be measured from a fixed date (e.g., year of birth or study entry) or age-specific mortality rates should be used rather than survival from diagnosis. Option B describes length-time bias (detection of slow-growing lesions). Option C is volunteer bias (healthy worker/healthy volunteer effect). Option D relates to overdiagnosis.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.