Why would any healthy person, newly diagnosed with cancer, elect not to have curative treatment? This reasonable question is often posed by patients who have newly diagnosed prostate cancer and are presented with the option of active surveillance. Communicating the answer to this question clearly is a crucial component of the active-surveillance strategy. The basis for this approach, the principles of patient selection and the indications for intervention during surveillance are reviewed in this article.

Active surveillance is an option for men with screen-detected, low-volume cancer. Patients with prostate cancer who fall into this category include men with a Gleason score of 6 or less, those with a prostate-specific antigen (PSA) value of 10 ng/ml or less and those with stage T1c or T2a disease. This definition encompasses about 45% of patients with newly diagnosed prostate cancer in a serially screened population. The concept is derived from the following five postulates: first, that screening for prostate cancer results in the detection of disease that in many patients is not clinically significant (i.e. if untreated, it would not pose a threat to health). Second, the patients who fall into this category can be identified with reasonable accuracy. Third, no treatment is minimal in terms of side effects and cost. Fourth, patients who are initially classified as low risk but who are reclassified over time as higher risk and treated radically are still cured in most cases. Finally, the psychological burden of living with untreated cancer has less impact on the quality of life than unnecessary, but curative, therapy.

Rational selection of patients for a surveillance strategy should be guided by these postulates. It is important to identify patients who have a low probability of disease progression during their lifetime according to clinical and pathologic features of the disease, patient age and comorbidity. Close monitoring of PSA levels and prostate pathology over time is essential. It is important that reasonable criteria for intervention are used, which will both identify patients with more-aggressive disease in a timely fashion and not result in excessive treatment, and to communicate appropriately with the patient, to reduce the psychological burden of living with untreated cancer