Zachary Klaassen: Hi, my name is Zach Klaassen, urologic oncologist at the Georgia Cancer Center in Augusta, Georgia. We're on UroToday at ASCO 2025 in Chicago. Delighted to be joined on UroToday by Dr. Ko Kimura, who is a nuclear medicine physician at UCLA. Ko, thanks for joining us on UroToday.

Koichiro Kimura: Thank you for having me today.

Zachary Klaassen: You have some great data you presented this weekend looking at PSMA PET predictors for selecting patients for lutetium and PSMA radioligand therapy. So maybe just tell our listeners why we need these predictors for selecting patients.

Koichiro Kimura: Sure. So several quantitative and visual PSMA PET/CT-derived imaging indicators have been proposed to predict treatment outcome of lutetium PSMA. But it's still unclear which indicator is the most reliable for clinical practice.

So recent guidelines from SNMMI and EANM clearly emphasize the importance of pretreatment PSMA PET/CT, but they don't specify which indicator should be prioritized for patient selection. So this gap motivates us to use data from US Expanded Access Program, or EAP, which provided lutetium PSMA therapy to patients with metastatic castration-resistant prostate cancer before FDA approved this treatment.

And EAP used inclusion criteria similar to VISION trial, but with more flexibility. So reflecting a broader real world setting. So this allows us to test imaging indicators in a practical setting.

Zachary Klaassen: Yes, absolutely. Great background. When we look at your study, maybe tell us how many patients-- what was the study design that you guys had for this?

Koichiro Kimura: Yes, it was an analysis of 88 metastatic CRPC patients treated with lutetium PSMA radioligand therapy in three institutions UCLA, UCSF, and Johns Hopkins. And we extracted the six imaging quantitative indicators from pretreatment PSMA PET/CT such as total tumor volume and SUVmean and SUVmax while using some specific software.

And we also assessed two visual indicators, like PSG and HIT score, and they are purely based on visual interpretation of PET scans. So without any specific special software. And these are recently proposed as a surrogate marker SUVmean. So we then evaluated how these imaging indicators associated with treatment outcome like PSA50, PSA progression-free survival and overall survival.

And finally, we then have these imaging indicators are performed when combining with a patient basic information like a patient age, baseline PSA, and so on. It's identified as to help understand how these imaging indicators can offer a prognostic value.

Zachary Klaassen: That's a great background of your guys' study. Tell us about the exciting results that you guys presented.

Koichiro Kimura: Key finding of our study is that-- so patients with high SUVmean tend to have great outcomes after lutetium therapy. And SUV is the average of amount of PSMA tracer absorbed by prostate cancer lesions on PET scans. And this gave us a sense of how strongly the tumor expresses overload.

We also looked at two visual indicators. But these imaging visual indicators did not show a strong association to treatment outcome in our group. I think that is because sometimes, like visual interpretation can be subjective and vary between leaders. So yeah, that is a reason.

And interesting like a combining with PET metrics, especially SUVmean with clinical variables improves survival prediction compared to a clinical variable alone model.

Zachary Klaassen: Excellent. And so when you think about the clinical implications, so quantitative being slightly better than visual, how does this disperse to the community? How are the implications of this data?

Koichiro Kimura: Yeah, that's a great question. So ideally, lutetium PSMA radioligand therapy works best when SUVmean is high and total tumor volume is low. But this favorable profile for this treatment is not captured by only like a serum PSMA level. So PSMA PET/CT is clearly of meaningful value to treatment planning.

And on the other hand, like a patient with low SUVmean and high total tumor volume may not respond lutetium PSMA as well. But we don't know still the best approach for them. So whether that's the combination with lutetium SUVmean with other systemic treatment or trying a different therapy altogether. So it is clear that more research is definitely needed in clinical trials and worldwide settings.

Zachary Klaassen: Yeah, that's fantastic answer. I think we've had so much excitement with the new indication for lutetium. I think your data really show the importance of the PSMA PET. Anything we haven't touched on, anything you want to concluding statements for our listeners.

Koichiro Kimura: If I had to leave one key point, it's a quantitative PET/CT, especially SUVmean can offer a meaningful value to clinical assessment. So it helps identify patients, most likely to benefit from lutetium PSMA and support better treatment planning. And we hope our findings help and wider adoption of these imaging indicators in both clinical trial and worldwide practice.

Zachary Klaassen: Great summary, Ko. Congratulations on the fantastic work, and thank you for joining us on UroToday. Great job.

Koichiro Kimura: Thank you so much.