Presenting manifestations, cigarette smoking, and detection bias in age at diagnosis of lung cancer

To examine the possible role of detection bias in the association between amount of cigarette smoking and age at diagnosis of lung cancer. The bias can occur because primary lung cancer can often escape detection during life and will be found (if at all) as a "necropsy surprise" unless a diagnostic workup is provoked by such presenting manifestations as hemoptysis and a localized chest lesion. The necropsy surprises will be reduced and the reported rates of pre-mortem incidence will be raised if a cigarette smoking history also acts as a diagnostic incentive.

This possibility was examined in a case series of 1266 patients whose primary lung cancer had been carefully classified according to diverse features at the time of presentation. For the total case group and for pertinent clinical, anatomic, and demographic subgroups, we then examined the trends for age at diagnosis in relation to amount of cigarette smoking.

The overall age at diagnosis (median = 63 years; mean = 61.2) remained essentially similar in five ordinal groups of Tumor, Nodes, Metastases (TNM) and four of five Clinical Severity stages, but had an inverse monotonic gradient in six ordinal groups of customary cigarette smoking [from none to >2 packs per day (ppd)]. Because an earlier age of discovery can be explained by either etiologic or detection-bias roles for heavier smoking, its impact was checked in subgroups with and without diagnostically provocative manifestations. In localized lesions, the smoking-age gradient vanished if suspicious "indicator" symptoms were present, but persisted if they were absent. Regardless of symptoms, the age gradient was strengthened in non-localized cancer lesions where smoking might particularly point to a primary diagnostic source in the lung.

Detection bias may play a distinctive, although often overlooked, role in the work-up decisions that precede and lead to a diagnosis of lung cancer.