Regular screening of individuals at risk of lung cancer may not reduce death from the disease.
This unexpected finding came via a long term follow up study (20.5 years) of the Mayo Lung Project. The original study, conducted between 1971 and 1983, was criticised for arriving at this same conclusion. While it was thought that an extended follow up might reveal a reduction in mortality from regular screening, this has not proven to be the case.
The reason is thought to be due to what is known as ‘overdiagnosis bias’. Regular screening may be revealing anomalies in the lung which have no significance in terms of patient lifespan.
However, once detected, the patient with such an anomaly is put on an ‘at risk’ list. The fact that patients generally do not die from such anomalies has long been taken as proof that screening works.
Study director Pamela Marcus, from the National Cancer Institute in Bethesda, Maryland, noted that the dangers of overdiagnosis in other cancers have already been recognised. Such over detection of cancers, especially given the new screening technologies available, may lead to unnecessary treatments that do more harm than good (J Natl Cancer Inst, 2000; 92: 1308-16).