PSA bounce after SBRT for bone metastasis

[Palex80]

Interesting case.

Patient with metastatic prostate cancer (several bone mets after prostatectomy and adjuvant RT).
He started ADT over 3 years ago and got up-front 6 cycles of Docetaxel. PSA dropped to around 1.5 ng/ml, remained stable for almost 2 years and rose this winter to 2.5 ng/ml.
Whole-body MRI showed a viable lesion in the spine, the rest of the lesions seemed stable. We had done yearly wbMRI, so it was rather easy to pick up.
I SBRTed the lesion and measured the PSA immediately prior to treatment delivery. It was at 2.7 ng/ml. Two months later he came back for a follow-up, PSA was 4.5 ng/ml. We were both disappointed, since it started looking like mCRPC, we decided to check the PSA again a few weeks later and schedule a new scan.
Now, four weeks later and the PSA dropped to 2.8 ng/ml (almost the same as prior to SBRT).
We hope it will continue to drop.

Was this a PSA-bounce caused by the SBRT? I know about PSA-bounces in primary RT of the prostate but have never seen one before when treating bone mets. Testosterone measured all the time, was always very low. My nuclear medicine friends say, they have seen that with Lutetium PSMA therapy a few times.

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[elementaryschooleconomics]

I'm cynical - with that 4.5 value, was it immediately repeated? I would be quick to point to lab error or variation as in, perhaps patient was mildly dehydrated, perhaps the flow cytometers in the lab hadn't been calibrated properly, perhaps the tech running the sample was having an off day, etc.

 

[ramsesthenice]

Interesting case.

Patient with metastatic prostate cancer (several bone mets after prostatectomy and adjuvant RT).
He started ADT over 3 years ago and got up-front 6 cycles of Docetaxel. PSA dropped to around 1.5 ng/ml, remained stable for almost 2 years and rose this winter to 2.5 ng/ml.
Whole-body MRI showed a viable lesion in the spine, the rest of the lesions seemed stable. We had done yearly wbMRI, so it was rather easy to pick up.
I SBRTed the lesion and measured the PSA immediately prior to treatment delivery. It was at 2.7 ng/ml. Two months later he came back for a follow-up, PSA was 4.5 ng/ml. We were both disappointed, since it started looking like mCRPC, we decided to check the PSA again a few weeks later and schedule a new scan.
Now, four weeks later and the PSA dropped to 2.8 ng/ml (almost the same as prior to SBRT).
We hope it will continue to drop.

Was this a PSA-bounce caused by the SBRT? I know about PSA-bounces in primary RT of the prostate but have never seen one before when treating bone mets. Testosterone measured all the time, was always very low. My nuclear medicine friends say, they have seen that with Lutetium PSMA therapy a few times.

First, wbMRI. Kudos. A third of my American patients don’t fit into a conventional MRI so I don’t see any future of that for us on this side of the pond. I assume you’ve never had to refer a patient to a veterinary school for an MRI? That’s always an awkward conversation. Use to have to do that in training.

Second, I have seen something like this once or twice before. Not sure it was ever a full 2 point bounce, but yes, I have seen a temporary bump after SBRT for a bone met. And, as you pointed out, it’s typically much sooner than after Xrt to the gland. No where near as common either. Sadly, when the number goes up in this setting, it usually stays up ☹️

 

[TheWallnerus]

Interesting case.

Patient with metastatic prostate cancer (several bone mets after prostatectomy and adjuvant RT).
He started ADT over 3 years ago and got up-front 6 cycles of Docetaxel. PSA dropped to around 1.5 ng/ml, remained stable for almost 2 years and rose this winter to 2.5 ng/ml.
Whole-body MRI showed a viable lesion in the spine, the rest of the lesions seemed stable. We had done yearly wbMRI, so it was rather easy to pick up.
I SBRTed the lesion and measured the PSA immediately prior to treatment delivery. It was at 2.7 ng/ml. Two months later he came back for a follow-up, PSA was 4.5 ng/ml. We were both disappointed, since it started looking like mCRPC, we decided to check the PSA again a few weeks later and schedule a new scan.
Now, four weeks later and the PSA dropped to 2.8 ng/ml (almost the same as prior to SBRT).
We hope it will continue to drop.

Was this a PSA-bounce caused by the SBRT? I know about PSA-bounces in primary RT of the prostate but have never seen one before when treating bone mets. Testosterone measured all the time, was always very low. My nuclear medicine friends say, they have seen that with Lutetium PSMA therapy a few times.

Think about PSA kinetics. Think about CaP Tpot and the cell death mechanism. Think about the amount of time between tPSA=2.7 and tPSA=2.8 (12 weeks?). Is a spinal SBRT dose 1) almost immediately cell-killing and 2) almost thoroughly cell-killing-complete at 12 weeks? It takes *some* contortion to make it all fit IMHO. I think it's a "cool story bro"

Not sure it was ever a full 2 point bounce, but yes, I have seen a temporary bump after SBRT for a bone met. And, as you pointed out, it’s typically much sooner than after Xrt to the gland.

A lot less dose causes more rapid cell kill to the same clonal line?

 

[Palex80]

I'm cynical - with that 4.5 value, was it immediately repeated? I would be quick to point to lab error or variation as in, perhaps patient was mildly dehydrated, perhaps the flow cytometers in the lab hadn't been calibrated properly, perhaps the tech running the sample was having an off day, etc.

It was repeated (by the patient himself) in another laboratory and showed even a higher value (I think it was 4.8 ng/ml).

 

[ramsesthenice]

A lot less dose causes more rapid cell kill to the same clonal line?

Maybe. I always thought the PSA bounce in the prostate had more to do with the prostate its self and not the tumor. Not sure anyone really knows.

 

[Palex80]

A lot less dose causes more rapid cell kill to the same clonal line?

Perhaps it's the type of cell kill that you are producing with SBRT compared to conventionally fractionated RT?

 

[Palex80]

Maybe. I always thought the PSA bounce in the prostate had more to do with the prostate its self and not the tumor. Not sure anyone really knows.

Indeed, the hypothesis is that PSA bounce is caused by an inflammation of the normal prostate and not by prostate cell death.

 

[TheWallnerus]

Indeed, the hypothesis is that PSA bounce is caused by an inflammation of the normal prostate and not by prostate cell death.

Is the hypothesis malleable... RT-related PSA bounce caused by normal prostate cells in the prostate, but prostate cancer cells when irradiating extraprostatically? Malleable hypotheses are hard to disprove.

 

[Mandelin Rain]

Think about PSA kinetics. Think about CaP Tpot and the cell death mechanism. Think about the amount of time between tPSA=2.7 and tPSA=2.8 (12 weeks?). Is a spinal SBRT dose 1) almost immediately cell-killing and 2) almost thoroughly cell-killing-complete at 12 weeks? It takes *some* contortion to make it all fit IMHO. I think it's a "cool story bro"

A lot less dose causes more rapid cell kill to the same clonal line?

My favorite Tpot

 

[evilbooyaa]

This is precisely why I do not check PSAs any earlier than a minimum of 3 months after end of RT for prostate cancer, no ifs, ands, or buts. If I don't re-image a brain until 3 months after b/c I'm worried about radiation inflammation/lack of maximal tumor response, then why would I check a PSA?

I presume the cells went crazy with their function, but didn't divide sufficiently leading to death, and thus shot out a bunch more PSA. Unless we're suggesting SBRT caused the cells to necrose and thus leak out all their intracellular stores of PSA immediately which then was already trending down by the time you checked at 2 months.

 

[Palex80]

Sorry for reviving this thread.
Today's PSA is 2.0 ng/ml (2.8 ng/ml 6 weeks ago).

 

[TheWallnerus]

Sorry for reviving this thread.
Today's PSA is 2.0 ng/ml (2.8 ng/ml 6 weeks ago).

How do you feel about this

 

[Palex80]

How do you feel about this

 

[evilbooyaa]

Sorry for reviving this thread.
Today's PSA is 2.0 ng/ml (2.8 ng/ml 6 weeks ago).