How common is undetected prostate cancer in older men?
With a low PSA and a negative MRI, around 5% of men still have prostate cancer. With a high PSA that figure rises to 38%, and the cancer that is missed often turns out to be aggressive.
PSA level and MRI result together broadly determine how likely it is that prostate cancer is present but has not yet been found. In men with a low PSA (2 to 3.9 µg/L) and a negative MRI, cancer was still identified within a year in only 5% of cases. That sounds reassuring, but it is not a guarantee.
The higher the PSA, the less reassuring a negative MRI becomes. At a PSA of 20 µg/L or above, prostate cancer was still found in 38% of men who had a negative MRI. A positive MRI gives a much clearer signal: at low PSA, cancer was found in 63% of those cases, and at high PSA (20 µg/L or more) in as many as 91%.
One striking finding: when cancer was discovered in a man with a negative MRI, it was high-grade, meaning aggressive, in 74% of cases. Among men with a positive MRI that figure was 80%. The difference is small. This means that a tumour missed on an MRI is not automatically a harmless, slow-growing one. A negative scan does not fully rule out aggressive cancer.
If you have a raised PSA and an MRI scan is carried out, discuss with your doctor what the result means in combination with your PSA level. Especially when PSA is high, a negative MRI result alone is not sufficient reason to skip further follow-up.
This answer is based on a single study that is not further indexed in the available sources. The findings on the combination of PSA level and MRI result are specific and internally consistent, but the strength of the evidence is limited because only one source publication is available. No additional independent confirmation from the other studies supplied with this question exists for this specific topic.