Have you had any treatment yet? If you’ve had a prostatectomy than a .21 is the point at which you should be getting salvage radiation or Start looking for spots with a pet test as you’ve already done.

The problem is that the pet test is not detecting metastasis below 2.7 mm, And according to a UCSF Radiation oncologist They have a problem, even if it’s 5 mm or less.

As a result, salvaged radiation may make sense. I had it and it gave me 2 1/2 more years before the cancer came back.

If you had radiation, then that is not a significant number.

Here are some information about when you should get salvage radiation if you’ve had a prostatectomy. This is from ASCO, They hold the major prostate cancer treatment conventions for doctors.

From Ascopubs about what PSA to do salvage radiation.
≤0.2 ng/mL:
Starting at this level maximizes disease control and long-term survival. Patients treated at PSA < 0.2 ng/mL achieve higher rates of undetectable post-SRT PSA (56-70%) and improved 5-year progression-free survival (62.7-75%).
Delaying SRT beyond PSA ≥0.25 ng/mL increases mortality risk by ~50%.
0.2–0.5 ng/mL:
Still effective, particularly for patients with low-risk features (e.g., Gleason ≤7, slow PSA doubling time). The Journal of Clinical Oncology recommends SRT before PSA exceeds 0.25 ng/mL to preserve curative potential.
0.5–1.0 ng/mL:
Salvage radiation remains beneficial but may require combining with androgen deprivation therapy (ADT) for higher-risk cases.