Unveiling the Promising Role of FAP PET Imaging in Accurate Bladder Cancer Staging - Domenique Escobar

June 6, 2023

Domenique Escobar discusses her study on Fibroblast Activated Protein (FAP) PET imaging for localized bladder cancer in this conversation with Wei Shen Tan.  She explains that FAP PET, a new diagnostic tool that targets proteins on cancer-associated fibroblasts, shows potential for more accurate disease staging and treatment pathways for patients. Compared to conventional imaging methods like CT, MRI, or FDG PET, FAP PET presents lower false-positive rates and demonstrates a higher specificity, especially for urothelial cancer. Dr. Escobar highlights that FAP PET could be useful across all stages of bladder cancer but may have the most impact at the pre-definitive treatment stage, potentially altering patients' treatment pathways. Though results from their pilot study are promising, Dr. Escobar emphasizes the need for larger studies to validate the effectiveness of FAP PET imaging.


Domenique Escobar, MD, Urologist, University of California, San Francisco, CA

Wei Shen Tan, MD, Ph.D., FRCS (Urol), Urologic Oncology Fellow, Department of Urology, MD Anderson Cancer Center, University of Texas, Houston, TX

Read the Full Video Transcript

Wei Shen Tan: So, good afternoon to our audience. Today, I have with us Dr. Domenique Escobar, a resident at UCSF. Dominique presented her presentation yesterday on FAP PET imaging in localized bladder cancer. So, congrats on your presentation, and could you tell us a little bit about your talk and what you found?

Domenique Escobar: Yeah, thank you so much for having me today. So, our presentation was looking at the use of FAP PET in patients with localized bladder cancer and FAP stands for fibroblast activated protein, which is a cell surface protein that's expressed on the surface of cancer-associated fibroblasts in the tumor microenvironment. Recently has been identified as an important target in diagnostics in many different kinds of cancer, including bladder cancer. So, our study was a small pilot study at UCSF as part of a clinical trial where multiple patients with different types of solid tumors were imaged. And this included 16 patients with bladder cancer, 10 of whom were localized at the time of imaging and plan to be treated with curative intent. So, that's kind of the summary of our project.

Wei Shen Tan: And in terms of performance of this FAP PET versus conventional FDG, what is the advantages that you found?

Domenique Escobar: Yeah, so compared to really all the types of staging imaging that we use for bladder cancer, whether it's CT, MRI or FDG PET, all have limitations in identifying metastatic disease and compared to other types of diseases, I think in bladder cancer, there really is a significant need for advances in imaging. So, that's something that's I think is really exciting about FAP PET. And some of the advantages include, it seems to have higher uptake in urothelial cancer compared to FDG PET. FDG PET can commonly have false positive lesions or inflammatory lesions that show uptake, and that doesn't seem to be as much of the case in FAP PET. And so, that kind of translates to a higher specificity of the imaging. And so, lesions that appear to be more inflammatory in nature, and that was confirmed on pathology where the pathology was negative, those lesions didn't show uptake in FAP PET. So, that seems to be one of the biggest advantages.

Wei Shen Tan: And in terms of performance, is it better for sort of equivocal lymph nodes or is it more visceral disease or bone? What did you find?

Domenique Escobar:
So, all of these areas do show uptake. Similar to other types of imaging, there can be false positives in the bone where there's uptake for lots of different kinds of reasons, whether it's degenerative or inflammatory or some other non-cancerous lesion. But it does seem to have a good uptake in lymph nodes and in the viscera.

Wei Shen Tan: I know not specifically relevant to your study, but what about the performance for urothelial versus other organs? Because you mentioned that this was part of a basket trial, that you had other cancer types, as well. So, any specific cancers that this might be more applicable to and how would you compare urothelial with these other type cancers?

Domenique Escobar: I don't have a lot of expertise in the use of FAP in other types of cancers. However, in the literature review that I've done, a lot of the studies have focused on colorectal and pancreatic cancer. And so, those studies show good performance in those types of cancers. But to be honest, I don't know too much of the details about other types of cancers.

Wei Shen Tan: And also, where would you see FAP PET being used? Do you see it as a screening tool in patients before they should undergo radical cystectomy? Or is it in the surveillance where you're going to pick up occult disease? Where do you see it being used in our bladder cancer patients?

Domenique Escobar: Yeah, so I think one of the things that's really exciting about FAP PET is that it seems it can be used kind of across the spectrum. In our cohort of 16 bladder cancer patients, including the 10 that were localized, we had patients really across the disease spectrum. So, it seems that it's useful across all different stages of disease.

What I think it's most useful for, however, is at the pre-definitive treatment stage. So, for example, one of our patients who appeared to be clinically localized on the localized imaging on the FAP PET was found to have widely metastatic disease. And that was confirmed on biopsy. And so, that patient's definitive therapy was really changed from radical cystectomy to systemic therapy. So, I think that is kind of where it has the most potential to really change patients' treatment pathways and ensure that people are getting the right treatment that they need and not unnecessarily undergoing things like cystectomy.

Wei Shen Tan: And in terms of the sensitivity, the performance of FAP PET in urothelial, what is it roughly based on your experience and small sample size?

Domenique Escobar: Yeah, the sensitivity appears to be very excellent because in our small series of 10 patients, the concordance with pathology was a hundred percent. And the specificity also appears to be excellent because these inflammatory lesions or false positive lesions on other types of imaging don't seem to show uptake on FAP PET, at least in our small sample.

Wei Shen Tan: Great. That seems very promising. So, before we conclude, could you summarize the key points of your findings for our audience?

Domenique Escobar: Sure. So, FAP PET or fibroblast activated protein PET is a new imaging modality that seems to show a lot of promise in a lot of different types of cancer, including bladder cancer. It has the potential to really change the treatment pathways for patients by ensuring that they're accurately staged and that their true disease status is really known before they undergo definitive therapy. So, the studies so far, and including our studies, have all been fairly small. Today, more small cohorts, small pilot studies, so I think it'll be really important to have some larger studies to continue to evaluate the performance of this new imaging modality.

Wei Shen Tan: Great. Thanks so much for your time. Thank you.

Domenique Escobar: Thank you for having me.