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Predictive power of PET PSMA scans

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User
Posted 05 Dec 2019 at 14:10

I wonder whether the latest PET scans can detect all potential metastases, and if not what’s the probability of some cells being missed?

Less than 5% ?

User
Posted 05 Dec 2019 at 15:45
I had a gallium 68 PSMA PET with psa 3 and it showed nothing. Having said that they are only just finding mets in me now at psa >200. I researched it quite a lot. The scan has amazing results in most men but does not work at all for up to 8% of men who actually have spread
User
Posted 21 May 2020 at 19:02

I posted in the conversation that I started that I will be getting the latest PSMA PET scan in a clinical trial in Canada. As I start to read more about the types of scans, I came across some articles that may be helpful.

From a PC blog - post is a few years old already, but gives some stats on detection rates at various PSA levels:
https://pcnrv.blogspot.com/search/label/PET%2FMRI

Here's a key part of the post:
Based on clinical trials, below are various PET indicators in approximate rank order of their sensitivity to detect prostate cancer, and their specificity for detecting it exclusively:
F18-DCFPyL
F18-DCFBC
Ga68-PSMA-HBED-CC (Ga68-PSMA-11)
Fluciclovine (F18 - FACBC)/ Axumin
C11-Choline/ C-11-Acetate
F18-Choline
NaF18
F18-FDG
The following table shows the percent of patients who had metastases detected at various PSAs. F18-DCFPyL is much better than Ga68-PSMA at low PSA. At PSAs between 0.5-3.5 ng/ml. it detected prostate cancer in 88% of recurrent patients, while Ga68-PSMA-11 only detected prostate cancer in 66% of the same patients - an improvement in sensitivity by a third.

Here's a more recent article comparing Ga68 to a number of different F18-labelled radiotracers:
18F-Labeled, PSMA-Targeted Radiotracers: Leveraging the Advantages of Radiofluorination for Prostate Cancer Molecular Imaging

Edited by member 21 May 2020 at 19:12  | Reason: Not specified

User
Posted 05 Dec 2019 at 16:16
No. as with any scan, cancer cells can't be seen unless they cluster to a minimum size. About 8% of men do not express sufficient PSMA to show up on a PSMA scan even if they do have tumours that would show up in other men. There is a correlation between increasing PSA, and tumour size and it being seen. So the chance of finding cancer in men with recurrence increases with higher PSA. The levels down to the size that can be seen can also vary with the type of PSMA scan being used.
Barry
User
Posted 05 Dec 2019 at 16:34

Originally Posted by: Online Community Member

I wonder whether the latest PET scans can detect all potential metastases, and if not what’s the probability of some cells being missed?

Less than 5% ?

Even with the new super tracers, the probability of cancer cells not being picked up will be much higher than 5% but unlikely to be any official figures as how can they measure how often something isn't seen? 

"Life can only be understood backwards; but it must be lived forwards." Soren Kierkegaard

User
Posted 21 May 2020 at 23:52

I read about the superiority of the F18-DCFPyL on an American forum several years back and with the 68 Gallium one so expensive in Europe contacted the Coordinator of the USA/Canadian trial to see whether they would scan me as there was a difference of opinion between hospitals as to whether an iliac node was cancerous. I was told that recruitment was being restricted to men of the two countries. Well, you can't win them all!!

Incidentally, following a 68 Gallium PSMA I had to pay for and a further MRI at UCLH, the balance of opinion was that the node was not affected but they found a small tumour of 3mm had grown in the prostate which was responsible for my low but persistently increasing PSA. A repeat MRI done in March 2020 has shown the tumour has increased by about 20% in a year. So good quality scans can, if the cancer is well concentrated, sometimes show even quite small tumours.

Edited by member 21 May 2020 at 23:54  | Reason: Not specified

Barry
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User
Posted 05 Dec 2019 at 15:45
I had a gallium 68 PSMA PET with psa 3 and it showed nothing. Having said that they are only just finding mets in me now at psa >200. I researched it quite a lot. The scan has amazing results in most men but does not work at all for up to 8% of men who actually have spread
User
Posted 05 Dec 2019 at 16:16
No. as with any scan, cancer cells can't be seen unless they cluster to a minimum size. About 8% of men do not express sufficient PSMA to show up on a PSMA scan even if they do have tumours that would show up in other men. There is a correlation between increasing PSA, and tumour size and it being seen. So the chance of finding cancer in men with recurrence increases with higher PSA. The levels down to the size that can be seen can also vary with the type of PSMA scan being used.
Barry
User
Posted 05 Dec 2019 at 16:34

Originally Posted by: Online Community Member

I wonder whether the latest PET scans can detect all potential metastases, and if not what’s the probability of some cells being missed?

Less than 5% ?

Even with the new super tracers, the probability of cancer cells not being picked up will be much higher than 5% but unlikely to be any official figures as how can they measure how often something isn't seen? 

"Life can only be understood backwards; but it must be lived forwards." Soren Kierkegaard

User
Posted 21 May 2020 at 19:02

I posted in the conversation that I started that I will be getting the latest PSMA PET scan in a clinical trial in Canada. As I start to read more about the types of scans, I came across some articles that may be helpful.

From a PC blog - post is a few years old already, but gives some stats on detection rates at various PSA levels:
https://pcnrv.blogspot.com/search/label/PET%2FMRI

Here's a key part of the post:
Based on clinical trials, below are various PET indicators in approximate rank order of their sensitivity to detect prostate cancer, and their specificity for detecting it exclusively:
F18-DCFPyL
F18-DCFBC
Ga68-PSMA-HBED-CC (Ga68-PSMA-11)
Fluciclovine (F18 - FACBC)/ Axumin
C11-Choline/ C-11-Acetate
F18-Choline
NaF18
F18-FDG
The following table shows the percent of patients who had metastases detected at various PSAs. F18-DCFPyL is much better than Ga68-PSMA at low PSA. At PSAs between 0.5-3.5 ng/ml. it detected prostate cancer in 88% of recurrent patients, while Ga68-PSMA-11 only detected prostate cancer in 66% of the same patients - an improvement in sensitivity by a third.

Here's a more recent article comparing Ga68 to a number of different F18-labelled radiotracers:
18F-Labeled, PSMA-Targeted Radiotracers: Leveraging the Advantages of Radiofluorination for Prostate Cancer Molecular Imaging

Edited by member 21 May 2020 at 19:12  | Reason: Not specified

User
Posted 21 May 2020 at 23:52

I read about the superiority of the F18-DCFPyL on an American forum several years back and with the 68 Gallium one so expensive in Europe contacted the Coordinator of the USA/Canadian trial to see whether they would scan me as there was a difference of opinion between hospitals as to whether an iliac node was cancerous. I was told that recruitment was being restricted to men of the two countries. Well, you can't win them all!!

Incidentally, following a 68 Gallium PSMA I had to pay for and a further MRI at UCLH, the balance of opinion was that the node was not affected but they found a small tumour of 3mm had grown in the prostate which was responsible for my low but persistently increasing PSA. A repeat MRI done in March 2020 has shown the tumour has increased by about 20% in a year. So good quality scans can, if the cancer is well concentrated, sometimes show even quite small tumours.

Edited by member 21 May 2020 at 23:54  | Reason: Not specified

Barry
 
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