Introduction
Lung cancer is the most common cancer worldwide. In 2008, the number of incident cases was estimated to be around 1.6 million (13% of all incident cancers). Mortality is high with 1.4 million of deaths the same year (18% of all deaths from cancer) (www.globocan.iarc.fr). Overall, survival rate at 5 years is <20% but heterogeneity is important and the search for prognostic factors has led to the publication of an impressive number of papers. However, due to the design and often retrospective nature of prognostic factors studies, few of these factors can really be used in routine care to guide management and to determine prognosis. More recently, with the development of so-called targeted therapies, more and more attention has been paid to the identification of predictive factors that might be better tools to guide therapy.
In the present paper, we will review how prognostic and predictive factors are different and how they can be identified. We will also present some well-known and important factors although we will not attempt at all to make an exhaustive report. This is virtually impossible; in 2002, Brundage et al. [1], in a systematic overview of prognostic factors for non-small cell lung cancer, identified 887 articles published during a decade and more than 150 possible prognostic factors for non-small cell lung cancer.
Prognostic versus predictive factor
A prognostic factor is generally defined as a factor, measured before treatment, that has an impact on a patient′s outcome “independently” of received treatment or of the general class of treatment. Populations of patients used for prognostic factors identification may be very broad (from resected stage I patients to stage IV patients scheduled to receive chemotherapy) or more specific such as patients treated with radical radiotherapy or stage III patients. Outcome is most often defined as overall survival but …
