When one is diagnosed with cancer the immediate reflex is often that they need treatment. However, for select men they not only need no treatment, they don’t need to even monitor their cancer. In fact, some of these men likely should not have been biopsied to even diagnose prostate cancer.
Who can undergo observation and not receiving treatment or being actively monitored? In general it is men with low risk prostate cancer who have a life-expectancy of <10 years. A large study done in the USA in elderly men demonstrated that there was no difference in how long men lived if they had surgery or had observation and no treatment for low risk prostate cancer.
This figure below is from the PIVOT study in men mostly over 60 years old, with 1/3 of men over 70 years old. About half of these men had a life expectancy of 10 years. This study compared surgery versus observation and showed that for only the low risk patients (shown in the figure below), there was no difference in how long men lived.