Population based studies of cancer survival: scope for the developing countries.

Survival refers to the life of a person after diagnosis of disease, and survival studies have the objective of evaluating the overall performance of a group of patients in terms of quality and quantity of life after the diagnosis or treatment. Potentially there are two approaches for the study of population-based survival; direct (classical) and indirect. The direct approach refers to defining a cohort of patients and collecting follow-up information, whereas the indirect approach uses current data on incidence and mortality for estimating various segments of life. In general, there are numerous difficulties in the conduct of population-based survival studies by the classical method, especially in the set-up of developing countries. These include time and finance required for the conduct of the study, the problem of loss to follow-up and also the time gap between the year of diagnosis of patients and the availability of results on their survival. In fact the problem of time gap is recognized even in the developed world. There have been many studies highlighting these problems and suggesting potential solutions. Generally they have focused on three directions: viz, improving the address information and thereby reducing the loss to follow-up; development of methodologies to deal with the losses to follow-up and indirect studies of cancer survival, thereby obviating the follow-up process. This commentary covers the potential approaches of population-based survival studies, classical survival studies, problems in the same, and methods adopted for their solution. A summary of the conceptual and methodological developments on these concepts, highlighting the scope for the developing countries, is also presented.