EAU guidelines and comments re Ga PSMA

[maley2711]

uroweb.org/guideline/prosta...

" Prostate-specific membrane antigen PET/CT has shown good potential in patients with BCR, although most studies are limited by their retrospective design. Reported predictors of 68Ga-PSMA PET in the recurrence setting were recently updated based on a high-volume series (see Table 6.3.1) [397]. Positivity rates in the prostate bed were significantly different in patients after RP (22%) and RT (52%). High sensitivity (75%) and specificity (99%) were observed on per-lesion analysis. "

NOTED THE MUCH HIGHER DETECTION RATE IN THE PROSTAE BED FOR RT..... 52%,,,,, THAN FOR RP.....22%. CONCERNING? EXPLANATION?? RT PROTOCOL TO REDUCE THIS NUMBER FOR RT?

Also noted this statement " In patients with BCR after RT biopsy status is a major predictor of outcome, provided the biopsies are obtained 18–24 months after initial treatment. Given the morbidity of local salvage options it is necessary to obtain histological proof of the local recurrence before treating the patient [923]." Also stated is that for RP, BCR does not require biopsy before salvage radiation> implying morbidity of salvage RT after RP is favorable compared to morbidity of salvage options after RT.

PSA (ng/mL) 68Ga-PMSA PET positivity

< 0.2 33% (CI: 16–51)

02–0.49 45% (CI: 39–52)

0.5–0.99 59% (CI: 50–68)

1.0–1.99 75% (CI: 66–84)

2.0+ 95% (CI: 92–97)

Study that includes this Table..........

pubmed.ncbi.nlm.nih.gov/273...

[Justfor_]

One possible explanation to your query is the difference in the definition of BCR between RP and RT. It looks like the former is more sensitive and catches it at an earlier stage compared to the latter. But the real blow is the lightness by which they administer blind RT to the prostate bed for such a small percentage of evidenced cases. Other studies that have seen the light gave a 1/3 chance for local reccurence at PSAs around 0.2.

[maley2711 in reply to Justfor_]

I'm not sure I follow. My understanding is BCR for RP is some very small rise from zero, or very close to zero post-removal. For RT, BCR is nadir + 2, correct? Why would that account for difference in detection in prostate bed? On your 2nd comment, you are saying they unnecessarily administer salvage RT after RP when PSA rises? why, in your mind,unnecessarily? Or is that not what you are saying?

Finally, what do you mean by "other studies that have seen the light" ?

[Justfor_ in reply to maley2711]

You understood me perfectly. The percentages quoted are not related to persons that had either primary treatment but to those that were classified as BCR. With RP almost the entirety of PSA is attributed to remaining PCa. With RT there is an unknown spread between benign and cancerous components. At a limiting spread of 90% bening to 10% cancerous the nadir plus 2 becomes equivalent to the 0.2 of RP. This 90-10% spread doesn't look realistic IMO. Consequently, patient's coming from RT were scanned at a more progressed phase. Taking also into account the PSA sensitivity ramp up, more detections seem reasonable again IMO. There is also a third reason that I am keeping to my self in order to avoid triggering an RP Vs RT war.

The two published studies breaking down the PSMA findings into classes in relation to the pre scan PSA come from California and The Netherlands. At a typical 0.2 post RP the detected lesions that will be caught by a blind sRT are only approx. 1/3 of the total. Your ref. mentions the prostate bed, but leaves out close by lymph nodes. It probably comes from the same sources.