Patients sometimes ask whether it's worth waiting for PSA to rise so that they can detect metastases with a PSMA PET/CT. The answer is "no."
PSMA PET/CT only detects 40% of the cancerous pelvic lymph nodes (LNs) that are detectable and about half of the bone metastases that are detectable. PET scans cannot detect anything smaller than about 5 mm, and 91% of all detectable metastases are smaller than that.
The current detection record for lymph nodes is set by USPIO 7T MRI, available only at Radboud University in the Netherlands:
The benefit is information, even if it is bad news. Better information hopefully leads to better decisions, updated SOC guidelines, and new ways to monitor progression or progress.
"Since each patient had both type of scans, the researchers could assess which type had more accurately detected those patients who had prostate cancer. The researchers found that MRI scans were significantly more accurate at detecting any grade of prostate cancer than the PSMA PET scans (0.75% for MRI vs 0.62% for PSMA PET)."
Interesting.
But I seem to remember that MRIs are best for one type of tissue and PET/CTs are best for aother type of tissue.
The benefit of bone scan/CT is that all the clinical trials that rely on the number of metastases used it. So, for example, if there are 0-3 bone metastases on a bone scan/CT, debulking the prostate is worthwhile no matter how many show up on a PET scan. Also, tracking progression is usually done with a consecutive bone scans. That's why it's still important to get one.
My understanding is that PSMA PET scans are useful for two reasons: 1) to determine whether the cancer has metastasized. 2) to find a met that may be causing pain so that it can be irradiated.
Once a patient is diagnosed stage IV (like me), finding more smaller mets is not going to change the treatment plan. In the 4.5 years since my diagnosis, I have never had a PSMA PET scan. There is no need. My annual bone and CT scans are good enough for now to monitor progression.
Yes. Dr Dorff told me the same thing when she saw I hadn’t had a PSMA PET: “We could do one now, but it wouldn’t change our treatment plan.” (Triplet therapy.)
Are you still maintaining the chart at the bottom?
3. I think there is another issue about waiting until your PSA rises to 2.0, before getting a scan. And it is not so much a medical issue as a personal one.
If you wait until you get to 2.0 PSA, you will be less inclined to worry that you got scanned too early and may have gotten false negatives.
In my case I held off on getting a scan until I reached 2.0. My rising PSA ended up stabilizing. And my Doc decided in the end not to do a scan.
I had 69 lymph nodes removed during my RP 4.5 years ago. Only one (which had previously been discovered with an Axumin scan) was positive. After surgery I swelled up like a balloon. Ongoing, I was left with mild to moderate lymphedema in my right leg. I do walk and exercise a lot, which definitely helps.
In my experience I had to wait until PSA hit a certain #. Now my insurance wants me to get a CT/bone scan before they will approve a PSMA PET, but I also want to know where my recurrence is to best choose how to treat and before it gets masked by ADT. Maybe I am mistaken but if the CT and Bone are negative the PSMA might not be and that would be relavant.
So, from a diagnostic setting, if the super sensitive PSMA PET Scan which is only 40% effective at detection of lesions 5mm and larger isn't that good, yet is the measure other imaging is compared too, what is then better?
Isn't 40% still better than nothing?
In discussion with my MO, who has noted with metastatic spread, the patient isn't treating PSA, but the metastatic characteristics of the disease. I agree as PSA is only basically a signal, a measure of one aspect of what may/might be occuring. Again, after reading so many studies that reference the G68-PET as the gauge to another tests efficacy, and that gauge being less than half effective itself, where are we?
Is this why oncology deflects to systemic therapy rather than targeting local spots or recurrences? Is this why absent systemic therapy the disease has a wide berth for spreading until all that less than 5mm lesions graduate and become detectable... There's definitely too much reliability placed upon imaging as a whole by patients as it being the tell-all answer to what's going on when it's not always the case. As noted, a combination of imaging using multiple layers, or, CT, MRI, Bone and PET, coupled with Blood and Genomic testing can provide a better peek under the covers so to say. I see a lot of newly diagnosed patients always hooting the miracles of Pet Imaging as being the answer to it all...
Is funny how as much as we think we know, we don't. How even when imaging has progressed, here, how Pet Imaging is amazingly sensitive as compared to years past what we could see, it still is not enough. Again, only 40% efficient compared to??? If Pet is superior to other testing then what where we seeing before... It's scary!
I read your post and responded to the 40% efficacy finding which is interesting. I agree somewhat to the conundrum of the not detected lesions eventually becoming evident at different times. What to do... What to do.
I just went through this very thing!
Recurrence, Castrate Resistance, some spots suspicious, low PSA producer along with low PSMA. What to do, especially because I've just completed a round (6) of Docetaxel just a year prior. Used the PSMA Pet scan but all the others (SOC) as well. Three suspicious locations, nothing jumping off the screen, what to do... I went with the Whack-a-Mole route knowing full well it was only treating what we "See" now. But that's for another thread, lol.
Anyways, I find it interesting how the 18F-DCFPyL study issues (from that original study) are always completely glossed over in comparison to G68-HBED-CC as the study which proclaimed it's superior efficacy noted the problems with the methodology. The fact that MORE agent was used vs the G68 and that in all probability the same results would have been observed if the comparative amounts had been used by both. So for myself, I will revert to G68-HBED-CC being superior until I read otherwise. It's problematic to ignore this as 18F comparative studies are then tainted? Is the lymphatic system prone to a cell type as well? Particular genomic markers... So much to consider.
I've had this discussion with my MO who shot down 18F testing at my request over G68... He told me straight out that it (G68) was better. I'm not saying the G68 is better though or best in all situations, my point entirely is that if it isn't so good, as noted, then where does that leave us? The best of the worst? Lol
You make reference to additional "future" contrasting agents being investigated... Do you have a list to share?
I believe if I know that the cancer is in my neck just under my skull I will probably not going to do BAT etc.
It would be too risky. Unfortunately the MO I am visiting for more than 4 years doesn't know that. He didn't read carefully the scan report. He believes that once I know that I am metastatic the whole purpose of the psma Pat scan is lost.
Thanks for the article. For some individuals the PSMA pet scan has been useful particularly if their cancer is PSMA avid and high Gleason grade . In a minority of cases it can detect lymph node involvement at a very early stage and therefore enable someone to get appropriate radiotherapy and systemic treatment earlier than otherwise.
Of the cohort of 532 men, 425 had a previous RP and 107 had prior radiotherapy. The median PSA of the RP group was 0.59 ng/mL and 5.8 ng/mL in the radiotherapy group. In the post RP cohort, the detection rate of 68 Ga-PSMA PET/CT was 11.3% for PSA 0.01 to <0.2 ng/mL, 26.6% for PSA 0.2 to <0.5 ng/mL, 53.3% for PSA 0.5 to <1 ng/mL, 79.1% for PSA 1 to <2 ng/mL and 95.5% for PSA ≥2. Lymph node metastasis post RP was identified in 68% of men with suspected disease recurrence. In the post radiotherapy cohort the detection rate was 33.3% for PSA 0.01 to <0.5 ng/mL, 71.4% for PSA 0.5 to <1 ng/mL, 93.3% for PSA 1 to <2 ng/mL and 100% for PSA ≥2.
ProPSMA 2020
The main read-out from the ProPSMA trial was the accuracy of the scans. The PSMA-PET scan was 92% accurate in detecting metastatic tumours (or the lack thereof), compared to only 65% accuracy for CT and bone scans.Accuracy relies on two measures, specificity and sensitivity:Specificity is the ability to correctly identify those without metastatic tumours (true negative rate). PSMA-PET identified 98% of men correctly who had no metastatic tumours. This was significantly higher than the 91% for CT and bone scans.Sensitivity is the ability to correctly identify those with metastatic tumours (true positive rate). PSMA-PET scans correctly identified 85% of men with metastatic tumours, compared to only 38% for CT and bone scans.
"A novel, nanotechnology-based scoring assay developed by researchers at Cedars-Sinai Medical Center was able to detect and characterize even microscopic amounts of prostate cancers, according to findings published in the journal Nano Today.
Prostate cancer is the most common cancer among men in the United States and the second most deadly cancer in US men, the authors noted. Thus, identifying new tests and interventions that serve this population is a research priority. The novel blood test is minimally invasive and could potentially help avoid unnecessary treatment and the resulting side effects."
An excellent post, thank you. This is why CT and nuclear bone scans must continue. And in my case a brain MRI caught 2-each, 2-mm tumors that would likely be missed by a lot of radiologists. (Gamma knife dealt with those tumors.)
Great post! Your point is well taken that there are different purposes for the utilization of different scans however none detect 100% of metastasis but I guess what’s important is what drives treatment or inclusion requirements for clinical trials. At MSK past few months had PET/CT PSMA( mild avidity ) ,FDG PET/CT , Bone scan, FDHTPET/CT ( for CC-94676 AR degrader research), CT scan in efforts to determine eligibility for clinical trials.
Why is there no known advantage to finding more metastases? What if the metastasis hasn't yet been identified and thus isn't being treated? Is "more" the operative word here?
My dad was diagnosed with PCa in 1999, Gleason 7, by rectal exam palpation since his PSA was normal. He had RP surgery in 2000 at MD Anderson where the surgeon cut through the tumor, leaving a significant amount behind. Path noted some cancer in a lymph vessel, but LNs were clear. Radiation followed. Ill health followed (had a post-op infection that was never adequately treated and still hasn't). Radiation damage (possibly in conjunction with Actinomyces odontolyticus and Strep. anginosus infections) later caused a fistula to develop between his urethra/bladder and his rectum. He underwent a double diversion in 2017 (urostomy with sigmoid neobladder and colostomy). PSA was undetectable until this past year and has slowly increased. When it crossed the threshold of 1.5, a PSMA/PET-CT was completed which showed essentially nothing. Plan is to just follow PSA for now which concerns me because it wasn't initially elevated and likely isn't a good marker for him. Genetic tests didn't show much.
Should we at least try the NaF18 PET/CT or not worth it? Is it worth trialing ADT?
In my case the PSMA scan was very valuable. I had PSA 2.7, Gleason 3+4. Bone scan, MRI, and ultrasound all showed no metastases. We were thinking watch and wait or RP. Then got a second opinion doctor that suggested PSMA scan which he called "the Hubble space telescope of prostate cancer scans." Surprise! Two lesions in the pelvis. "Good thing you didn't do the surgery" he said and we started SBRT.
Since the cancer had already spread outside my prostate removing only the prostate by surgery would have left some cancer behind, still in my pelvis. The radiation I received was aimed at 3 targets: prostate and the 2 lesions in my pelvis.
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