PSA of 27

This is actually for a friend of mine. He has a rising PSA that stands at 27. Has had 2 biopsies and MRI's a year apart that show no lesions or anomalies. The doctors are sort of perplexed at this point.
Any suggestions as what he can ask his doctor? Has anyone seen something similar?

Would a PSMA test show something that a biopsy or MRI miss?

Thanks for any suggestions