And as other commenters have noted, early detection does not mean the ultimate outcome will be improved -- some cancers have a spectrum of presentations, with some persons having more slowly growing / indolent tumors that can be detected and treated (but may not have actually been likely to harm the person harboring the lesion), while other persons develop rapidly growing and very aggressive tumors that will be fatal (but are hard to detect with screening because they develop and spread rapidly). Only carefully constructed and controlled studies can determine if screening for a particular cancer with a particular screening test actually improves survival or reduces morbidity -- short term or uncontrolled studies can be very misleading.
Also the whole subject is subject to anger and political correctness issues -- some good hearted persons want to believe that some screening metholodogy must help because they want it to help, the evidence be damned! So there can be more heat than light ... anybody who says a specific screening test not helpful can be accused of running a "death panel".
Prostate cancer: (not effective) http://summaries.cochrane.org/CD004720/screening-for-prostat...
Breast cancer: (evidence conflicting, minimal improvement) http://summaries.cochrane.org/CD001877/screening-for-breast-...
And as other commenters have noted, early detection does not mean the ultimate outcome will be improved -- some cancers have a spectrum of presentations, with some persons having more slowly growing / indolent tumors that can be detected and treated (but may not have actually been likely to harm the person harboring the lesion), while other persons develop rapidly growing and very aggressive tumors that will be fatal (but are hard to detect with screening because they develop and spread rapidly). Only carefully constructed and controlled studies can determine if screening for a particular cancer with a particular screening test actually improves survival or reduces morbidity -- short term or uncontrolled studies can be very misleading.
Also the whole subject is subject to anger and political correctness issues -- some good hearted persons want to believe that some screening metholodogy must help because they want it to help, the evidence be damned! So there can be more heat than light ... anybody who says a specific screening test not helpful can be accused of running a "death panel".