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Devaki Surasi: Hello everyone. I'm Shilpa Surasi, a nuclear medicine physician and radiologist in the Division of Diagnostic Imaging at MD Anderson Cancer Center Houston. I'll be presenting the next case in the joint collaboration of SNMMI and UroToday on a case with localized prostate carcinoma with discordant findings on multiparametric MRI and PSMA PET.

Let's start off with the patient background. This is a 54-year-old male presenting with a PSA of 24.9 ng/mL. A biopsy was performed of the prostate gland, which demonstrated prostatic adenocarcinoma with a Gleason 7 (4 + 3) in eight out of the 13 cores. A CT abdomen and pelvis and a bone scan were performed, which were negative.

Now let's look at the findings of the multiparametric MRI pelvis. On the top panel you see the coronal T2 and the axial T2 weighted images. You can see that there is diffuse hypointense lesion in the left and the midline portion of the prostate gland extending from the base to the apex.
This is the section on the axial images where you see the same lesion with extension beyond the prostate gland, so there's extraprostatic spread, and also involvement of the seminal vesicles left greater than the right.

On the bottom panel here are prostate images with the deficient rated image here, again showing abnormal signal with hypointense signal on the ADC images, but corresponding contrast enhancement on the post-contrasted images.

Next, the patient underwent a PSMA PET/CT study. On the left-hand side is the mid-image, and I'd like to focus your attention to the axial images on the right side. The top panel is at the level of the prostate gland, and you can see that there is not really a lot of PSMA activity within the prostate corresponding to the areas of signal abnormality seen on the MRI.

The bottom panel are the axial images at the level of the seminal vesicles, and you can see that there is very mild activity corresponding to the left seminal vesicle, which again corresponds to the area of abnormal signal abnormality on MRI.

Here I present a axial cut at the level of the obturator nodes, which were slightly prominent, but there is really no activity corresponding to the nodes. This patient was presented at the multidisciplinary tumor board and treatment was decided, which was initiation of androgen deprivation therapy with a loading dose of degarelix, intensification of hormonal therapy with a second-generation AR targeting agent after two weeks of ADT, and maximal cytoreduction over a period of four to six months, followed by surgical consolidation treatment.

This case highlights that there are a small subset of prostate cancer patients who do not really express PSMA, and are negative or are less avid on PSMA PET imaging, and the possible reasons could be intratumoral heterogeneity, variation in the intensity of PSMA expression, neuroendocrine differentiation, and also depends on the extent of the disease, so the tumor volume.

While PSMA is an important imaging modality for prostate cancer, complementary imaging approaches to detect and characterize PSMA-negative lesions should be considered. It has been shown that PSMA-suppressed tumors upregulate amino acid transporters, and this may be exploited through ¹⁸F-fluciclovine PET imaging.

Secondly, while FDG PET is not widely used to detect prostate cancer due to its relatively low diagnostic efficiency, it still has a value in a subset of patients with poorly targeted adenocarcinoma.

Lastly, targeting cancer associated fibroblasts with fibroblast activation protein inhibitors, or FAPI-based radiotracers, have shown promising results in the diagnosis of various types of cancers, including prostate cancer, and this could potentially be one of the tracers that could be used in cases where PSMA PET is negative.

With that, I thank you for your attention, and I'd also like to thank the SNMMI Prostate Cancer Outreach Working Group members. Thanks for watching.