Now, scientists reporting in the journal Lancet Oncology say they have found two distinct genetic "signatures" for prostate cancer.
These signatures may help predict which patients have aggressive tumors.
The idea would be to design experimental blood tests to read those genetic signs, almost like passing a barcode over a scanner.
Researchers say reading these signs in the blood could more accurately detect which prostate cancers are mild or aggressive.
Treatment plans could then be adjusted based on the findings.