Incidental lung cancers identified at coronial autopsy: implications for overdiagnosis of lung cancer by screening.

The extent to which overdiagnosis occurs in lung cancer screening programmes has been debated. Overdiagnosis refers to the detection by screening of cancers that would not have become clinically apparent or symptomatic before that individual died of other causes. A retrospective review of coronial autopsies performed in Victoria between April 1991 and February 2002 was conducted to determine the rate of incidental lung cancer in individuals who died of natural causes. A total of 24,708 autopsy reports were searched electronically. We estimated that in 56% of these death was from natural causes. Amongst individuals who died naturally there were 167 cases of lung cancer, 47 of these were incidental including five carcinoid tumours, three small cell tumours, 11 cases of carcinoma in situ and 28 invasive nonsmall cell lung cancers. Of the incidental invasive nonsmall cell lung cancers, 86% were stage I. Although incidental lung cancer is uncommon, there are some lung cancers that remain undetected during life and do not contribute to death. These findings support the hypothesis that some lung cancers detected by screening may never progress to cause symptoms or death in that individual's lifetime and therefore may be overdiagnosed by screening.