The Usual Course of Prostate Cancer
Most diseases have four stages:
- Biological changes begin, but cannot yet be detected.
- The disease progresses to the point at which changes can be detected, but there are no symptoms yet.
- The disease progresses to the point where symptoms appear.
- The disease runs its course and reaches its final outcome (recovery, disability, or death).
The stages vary in length with different diseases, and with different people with the same disease. The usual course of prostate cancer is not very well understood, at least in terms of predicting if and when it will move from one stage to the next. A large proportion of cases never develop past stage 1 or 2. But some do progress quite rapidly and, often, are already advanced beyond the curable stage when symptoms appear.
For most diseases there is a critical point at which therapy is most effective. This could be at or between any of the first three stages. Screening occurs at stage 2, when the disease can be detected but before symptoms are present. Therefore, screening is effective only when a disease has a critical point at this stage.
