Earlier detection with screening makes a difference in only a small subset of cancers – those that grow slow enough that they can be detected before they spread yet fast enough that they would’ve spread exactly between the time it is detected by acreening and become apparent; some cancers are so slow-growing that they may not even spread within one’s lifetime. In case of prostate cancer, it is not even clear if screening helps at all.

To help you understand the statistics: over 70% of women would survive breast cancer even without screening; out of those who die the frequently-cited 30% mortality reduction (optimistic) means that out of 10 women who would’ve died of breast cancer without screening, 7 will still die even with screening. In absolute numbers it means that if you are in your 50s and screened for 10 years, you have 1/500 chance that it’ll help you. This is an optimistic number, USPSTF cites 1/1200. During the same time you have over 50% chance of having at least one false positive; about 1/4 of these false positives will end in biopsy. Also because of the detection of leisions that would’ve not spread if remaned undetected, you have a somewhat higher chance of being diagnosed with breast cancer, being treated and suffering side effects of treatment (overdiagnosis). The estimates of overdiagnosis vary between 4 and 30% of all detected cancers.

The more accurate the test, the higher the probability of false positives and overdiagnosis.

Emotions and personal preferences aside, what I’d be interested to know is the impact of these false positives on heart desease. Stress is bad for you, some people’s blood pressure skyrockets during false positive, false positive evaluation, etc. None of the studies showed (and had statistical power to show) any effect on all-cause mortality…