system
Given the following post, respond as if you're commenting on Reddit:
human
In clinical oncology, why is cure defined as survival at 5 years? Is there something about the 5 year mark that is special compared to 1, 2, or 10 years?
gpt
In oncology, the standard metric that is used is "5 year survival"-- this isn't the same as claiming that after 5 years someone is cured. 
 
5 year survival rates are simply the percentage of people with a specific type of cancer who are still alive 5 years from their diagnosis. This allows for comparison of cancers (e.g. pancreatic cancer has a very low 5-year survival rate, while early stage breast cancer has a very high 5 year survival rate.  

So nothing magical about 5 years, it just allows for comparisons across many cancer types. Since survival rates have been improving for many cancers, you may start to see 10-year survival rates being reported more frequently.