Prostate cancers are very heterogeneous. Just like you can have prostate cancers, one a Gleason 6, one a Gleason 7, and another a Gleason 8, similarly one cancer might express a lot of PSMA, one a little, and another none at all. It’s very heterogeneous,
Normally (but not always) the more aggressive the prostate cancer, the more PSMA expression it has (measured by its SUVmax score). Your Gleason 8 should’ve (but, not always) expressed a lot of PSMA.
Your medical oncologist indicated there was uptake; what was the SUVmax score they assigned to that uptake?
The background, non-cancerous tissues they compare to are the blood, liver, and parotid (salivary) glands that express low, medium, and high levels of PSMA, respectively, without being cancerous . They assign SUVmax values to those (which should be indicated in your PSMA PET scan report); then they compare those scores to the SUVmax scores they’ve assigned to any cancerous lesions that “light up.”