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Advanced Prostate Cancer

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Confused about which scan is more suitable

traveller64 profile image
13 Replies

Some cancers express a lot of PSMA while other cancers express very little or no PSMA. So how do we know which scan is more suitable to detect metastasis; Ga68 PSMA or FDG PET?

Could it be that nothing shows up on a PSMA PET but cancer is detected on FDG PET or vice versa?

If this is true, then how do we know which scan is more suitable? I guess it is not wise to have both scans at the same time

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traveller64
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Javelin18 profile image
Javelin18

There’s a good deal of discussion on this topic. Tall_Allen has posted a link to an overview. He is more eloquent than me, so I’ll let him respond.

User slpvnmd posted this in response to one of my posts

Three links to PET imaging in Prostate Cancer. No real consensus but I firmly believe knowledge always helps. clincancerres.aacrjournals.... ncbi.nlm.nih.gov/pmc/articl... pubs.rsna.org/doi/pdf/10.11... 18F-Fluciclovine is Axumin PET

Javelin18 profile image
Javelin18 in reply to Javelin18

Looks like pasting the links didn’t work. Take a look at the post “Damn PSA” for Tall_Allen’s advice and the links provided by slpmvdmd. (I think I spelled the username correctly)

GP24 profile image
GP24

You need a PSA value well above 10 ng/ml to detect cancer with an FDG PET/CT. This is no problem if you have done all available therapies and nothing works any more. If you are not in this situation you better get a PSMA PET/CT which will usually detect cancer if the PSA value is above 1 or 2 ng/ml. If you suspect PSMA negative tumor, you could get a Choline PET/CT. However, for that your PSA should be above 5 ng/ml. It is different, if you are on Lupron. Then theses scans can detect tumor at lower PSA values.

Tall_Allen profile image
Tall_Allen

If you are still early in progression, it is unlikely that anything will show up on an FDG PET. But if you are later in progression, the cancer may be less PSMA avid and may uptake more FDG. They can be done on consecutive days (FDG requires fasting).

traveller64 profile image
traveller64 in reply to Tall_Allen

If you are early in progression, is the tumor generally PSMA avid?

Tall_Allen profile image
Tall_Allen in reply to traveller64

There seems to be an optimal point - PSMA doesn't rise to the cell surface if too early; cancer cells lose PSMA expression if too late. The Goldilocks moment probably differs across patients. I think Dr.Calais has a clinical trial to see if hormone therapy can be used to increase PSMA expression short-term (as in lab studies).

traveller64 profile image
traveller64 in reply to Tall_Allen

Thanks Allen. So if cancer cells do not express PSMA, then which scan would be suitable?

Tall_Allen profile image
Tall_Allen in reply to traveller64

It depends how far along you are in progression. FDG, if much farther along. NaF(18) is MUCH better at detecting bone metastases than PSMA. There are many experimental radiotracers.

EdBar profile image
EdBar

During my recent visit with Dr. Sartor who is one of the authors of the Vision trial and someone who is obviously very well versed in PSMA scans felt that a PSMA scan was the optimal scan to get. In fact for someone like me who is heavily treated and just starting to see a rise in PSA after several years of cancer dormancy he is likely to recommend me getting one at lower PSA levels than what is typical. Normally he would wait until PSA reaches 0.5, but in my case 0.1 was the number due to the treatments I’ve undergone. His thought was that PSA could be suppressed after years of treatment.

Ed

traveller64 profile image
traveller64 in reply to EdBar

Thanks Ed. Did you find anything on the PSMA scan at 0.1 psa?

EdBar profile image
EdBar in reply to traveller64

Haven’t had it yet. Latest PSA was 0.05, ya I know that’s really low, but it was undetectable for about 6 years. I like being proactive and Sartor feels the same way. If they can find the source perhaps we can hit it with SBRT, I recently had Provenge treatment so those two would work nicely together.

jjpeabody profile image
jjpeabody in reply to EdBar

Hi EdBar, my PSA was 0.12 when the PSMA SCAN detected tumor in surgical bed. On my recent anual CT lung scan a 5mm nodule showed up in right lung, previous smoker and 71. Looks like I'll have a needle biopsy prior to SRT with WPLN. Good luck all.

j-o-h-n profile image
j-o-h-n in reply to jjpeabody

If lung test positive: GO FOR KEYTRUDA!!! (no cutting)....

Good Luck, Good Health and Good Humor.

j-o-h-n Friday 12/03/2021 8:18 PM EST

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