A randomized trial of lung cancer screening with low-dose CT reports that screen-detected cancers have significantly better 5-year survival than clinically detected cancers, yet cause-specific mortality is unchanged. The most likely explanation for this discrepancy is:
- A Length-time bias favouring detection of slow-growing tumours
- B Overdiagnosis, with detection of indolent lesions that would never have become clinically apparent ✓
- C Recall bias in ascertainment of the date of diagnosis
- D Selection bias because volunteers for screening are healthier than non-volunteers
Correct answer: B. Overdiagnosis, with detection of indolent lesions that would never have become clinically apparent
Explanation
When survival improves but cause-specific mortality does not, the classic explanation is overdiagnosis: screening detects pseudodisease, such as indolent tumours that would never progress to symptoms or death. Length-time bias also inflates apparent survival, but it operates through preferential detection of slowly progressive cases among those that do progress, whereas overdiagnosis counts lesions that were never destined to matter. Volunteer bias affects observational comparisons, not a randomized trial.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.