FDG pet scan not the best for prostat... - Advanced Prostate...

Advanced Prostate Cancer

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FDG pet scan not the best for prostate cancer ?

joeguy profile image

It has been recommended on here that an FDG pet scan is a wise companion scan to have with a PSMA scan to see overlap between the two. When discussing this with my doc recently he was of the opinion that an FDG pet is not very good at picking up prostate cancer compared to some of the other pet scans available. If this is true, what is the best pet scan to have other than a PSMA scan ?

23 Replies

Without ADT your PSA value should be above 10 ng/ml for a FDG PET/CT. With ADT it is difficult to predict. You could get a Choline PET/CT instead.

You could get a Lu177 therapy and if this does not work, get a FDG PET/CT to check why.

joeguy profile image
joeguy in reply to GP24

Was hoping to be able to use the PSMA and some other pet scan to determine if LU177 is likely to work or not. I am on ADT and PSA is currently 1.49 and rising. If the rate of increase holds, I should be at 2.0 - 3.0 in August when I have my next blood work done.

GP24 profile image
GP24 in reply to joeguy

In the TheraP trial by Dr. Hofman they screened 291 patients and 51 of these were excluded because of disconcordant mets on PSMA PET/CT and FDG PET/CT. So you have a good chance that Lu177 will work.

Consort diagram for key details of the TheraP trial

From January:

pubmed.ncbi.nlm.nih.gov/349...

68Ga-prostate-specific membrane antigen (68Ga-PSMA) PET/CT is a commonly used imaging modality in prostate cancers. However, few studies have compared the diagnostic efficiency between 68Ga-PSMA and 18F-FDG PET/CT and evaluated whether a heterogeneous metabolic phenotype (especially 68Ga-PSMA-negative [-], 18F-FDG-positive [+] lesions) exists in patients with castration-resistant prostate cancer (CRPC). We determined the added value of 18F-FDG PET/CT compared with 68Ga-PSMA PET/CT in CRPC patients and identified CRPC patients who may benefit from additional 18F-FDG PET/CT.

Methods: The data of 56 patients with CRPC who underwent both 68Ga-PSMA and 18F-FDG PET/CT from May 2018 to February 2021 were retrospectively analyzed. The patients were classified into 2 groups: with or without 68Ga-PSMA-, 18F-FDG+ lesions. The differences in patient characteristics between the 2 groups and predictors of patients who have at least 1 68Ga-PSMA-, 18F-FDG+ lesion were analyzed.

Results: Although both the detection rate (75.0% vs. 51.8%, P = 0.004) and the number of positive lesions (135 vs. 95) were higher for 68Ga-PSMA PET/CT than for 18F-FDG PET/CT, there were still 13 of 56 (23.2%) patients with at least 1 68Ga-PSMA-, 18F-FDG+ lesion. Prostate-specific antigen (PSA) and the Gleason score were both higher in patients with 68Ga-PSMA-, 18F-FDG+ lesions than in those without (P = 0.04 and P < 0.001, respectively). Multivariate regression analysis showed that the Gleason score (≥8) and PSA (≥7.9 ng/mL) were associated with the detection rate of patients who had 68Ga-PSMA-, 18F-FDG+ lesions (P = 0.01 and P = 0.04, respectively). The incidences of having 68Ga-PSMA-, 18F-FDG+ lesions in low-probability (Gleason score < 8 and PSA < 7.9 ng/mL), medium-probability (Gleason score ≥ 8 and PSA < 7.9 ng/mL or Gleason score < 8 and PSA ≥ 7.9 ng/mL), and high-probability (Gleason score ≥ 8 and PSA ≥ 7.9 ng/mL) groups were 0%, 21.7%, and 61.5%, respectively (P < 0.001).

Conclusion: Gleason score and PSA are significant predictors of 68Ga-PSMA-, 18F-FDG+ lesions, and CRPC patients with a high Gleason score and PSA may benefit from additional 18F-FDG PET/CT.

He is right and wrong. FDG is not very good at picking up prostate cancer initially, but eventually the prostate cancer evolves to digest glucose (the G in FDG stands for Glucose). Pluvicto, as currently approved by the FDA, is only approved among patients who have failed chemo and a 2nd line hormonal - some have progressed to the point where much of their cancer no longer expresses PSMA and has begun to digest glucose. When there is a lot of these mixed cancer types, destroying only the PSMA-avid cancer, just gives the FDG-type cancer (which is more aggressive) more room and nutrients to grow. It can actually make the cancer worse - we see this in some men treated with Pluvicto - growth seems to accelerate. It is prudent to do both.

prostatecancer.news/2019/12...

joeguy profile image
joeguy in reply to Tall_Allen

Thanks Allen,Im am in the process of failing 2nd or 3rd line hormonal, but I was hoping to try Lutetium treatment before chemo, if I do chemo at all (I watched chemo kill my father). The FDA is a real pain in the butt, and I certainly question much of their "wisdom".

Tall_Allen profile image
Tall_Allen in reply to joeguy

The FDA is only by law allowed to approve what was tested. As more situations are tested, there will undoubtedly be more indications approved. There are ongoing clinical trials for new indications.

Did your father have chemo for prostate cancer?

joeguy profile image
joeguy in reply to Tall_Allen

No, his PC was treated successfully with Brachy back in the 90s. He later developed colon cancer, and it was the chemo they gave him for colon cancer that killed him.

Tall_Allen profile image
Tall_Allen in reply to joeguy

They give a very powerful chemo cocktail for colon cancer, not at all like what is given for prostate cancer.

joeguy profile image
joeguy in reply to Tall_Allen

Yes, it was a cocktail of 3 different chemo drugs. I certainly have not ruled out chemo, I am just very apprehensive.

Fightinghard profile image
Fightinghard in reply to joeguy

There is a trial now called SPLASH. Looking for post hormone but pre chemo participants. I am hoping to get a shot at Pluvicto in a couple weeks. You might ask your MO to help you find a local treatment center that is part of this trial

joeguy profile image
joeguy in reply to Fightinghard

Thanks, I hadn’t come across that one yet. It might be perfect for my situation

Great discussion above. I would only like to add that prostate cancer starts using Sugar at very late stage as it uses Glycolytic pathway . FDG scan records sugar related Metabolic activity and will light up those mets which are now using sugar as their main fuel. Rather than FDG scan, it is better to get a Tc Bone scan (most sensitive but less specific) to compare.

joeguy profile image
joeguy in reply to LearnAll

Interesting..... how do you know if you are late stage enough to use sugars ?

anonymoose2 profile image
anonymoose2 in reply to LearnAll

I have ask when the PC starts feeding off sugar will doctors start prescribing medications to lower the sugar to slow the progression of PC?

joeguy profile image
joeguy in reply to anonymoose2

I just recently learned that PC feeds off sugar in the later stages. I may need to cut out the cheese cake ☹️

Publix bakery here in FL has a pretty good sugar free N.Y. Style Cheesecake

One clue to change in fuel from fatty acids to Glucose is happening is to check serum LDH which is an enzyme in Glycolytic pathway. As cancer cells start switching from use of Fat to use of Sugar, this enzyme (LDH) starts rising in blood. This change in fuel by PCa is a gradual process but in aggressive variants it can start very early on.One needs to monitor Serum LDH . Its little complex to interpret LDH result if one has other comorbid chronic illness . A low normal LDH is a good sign and indicates that excessive tissue damage is not occurring.

Per the retrospective analysis that pjoshea posted above, with your Gleason 4+3 and PSA well below 7.9 , you would have a Zero % chance of having a PSMA-, FDG+ lesion anyway. Though that does not prove it for you as an individual. Personally, I would get the FDG scan for completeness.

You have been considering Lu treatment for at least two years now, and we know it works better sooner than later. (Strong indications anyway.) And especially for lymph node mets.

So it would seem prudent now to either proceed with the chemotherapy, for whatever benefit it can offer in slowing the disease, and make you at least eligible for Pluvicto. Or go abroad for Lu-PSMA treatments now if you can afford to do so.

Just trying to clarify perspective for you dear friend.

As it turned out, my Gleason score was not accurate at all. The pathology after the RP showed large areas of grade 5 cancer not found in the initial biopsy. I have been considering going overseas for Lu treatment, just not sure I can afford it at this point. With the FDA only allowing Lu treatment after chemo, I am left with trying to get into a trial, which I was working on before the "supply chain shortage" hit the Lu supply. Sounds like supply is starting to resolve, so back to trial hunting for me. Although, I will have to wait for PSA to rise over 2.0 to be eligible for most trials. This should happen by August.

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

Cheesecake? Did someone say Cheesecake? New York Cheesecake? Please dial 911......

Good Luck, Good Health and Good Humor.

j-o-h-n Wednesday 06/22/2022 7:17 PM DST

Great question

A lot of good info here. I just want to emphasis so it doesn't get lost the importance of what Tall Allen stated in regards to getting both the PSMA scan AND the FDG pet scan.

When there is a lot of these mixed cancer types, destroying only the PSMA-avid cancer, just gives the FDG-type cancer (which is more aggressive) more room and nutrients to grow. It can actually make the cancer worse - we see this in some men treated with Pluvicto - growth seems to accelerate. It is prudent to do both.

Getting the FDG pet can avoid what is sometimes termed "repopulation" of the cancer cells and the acceleration of growth.

Also confirms if Lu-177 has a chance of some success or not.

I would not IMHO use the treatment because "it worked in some men".

I would get the treatment if both scans indicated benefit and safety from repopulation.

After the trial that noted it worked in X amount of men and not others it was determined that getting a FDG pet was critical in knowing if it would have benefit or not.

This information is very helpful in understanding:

prostatecancer.news/2019/12...

I don't know your age or health conditions but if chemo is in the cards it is not so bad for most of us. You can do one infusion at a time and quit if you want to.

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