Biological Variation of Tumor Markers and Its Application in the Detection of Disease Progression in Patients with Non-Small Cell Lung Cancer (Technical Briefs‪)‬

Patients with advanced non-small cell lung cancer (NSCLC) may benefit from chemotherapy (1, 2). This type of treatment is highly toxic and expensive, and patients should be monitored to detect those in whom the disease progresses despite treatment to avoid ineffective treatment and a loss of quality of life. Tumor markers are useful for detecting progression in cancer patients undergoing chemotherapy (3, 4), but there are no uniform criteria establishing how large a difference between two consecutive measurements should be to indicate progression of the disease. The first step in dynamic assessment of a specific biological constituent is to define the difference between two consecutive results that indicates a change in the patient's health status. The most widely accepted approach for this purpose is the so-called reference change value (RCV), a concept described by Harris and Brown (5). Using serial analytic results from the same individual, it is possible to calculate the RCV that defines the critical difference between two consecutive results for a constituent at a specific probability. The RCV encompasses both biological and analytical variation and has been determined for several constituents in healthy patients and in some diseases (6-14).