Oliver Sartor: Hi, Dr. Oliver Sartor here with you today. We're at the third annual Prostate Cancer Consensus Conference in Colorado Springs. And really delighted to have two special guests here today. Dan Petrylak, professor of Medicine Neurology at Yale Smilow Cancer Center, and Dr. Neeraj Agarwal at the University of Utah. And you do many things at University of Utah in addition to being a professor, but welcome both.

Neeraj Agarwal: Thank you.

Oliver Sartor: So we're going to talk about SPOP. Now, I don't know if everybody in the audience even knows what this gene is about. So let's talk a little bit about what is this SPOP gene, or some people call it SPOP, I'm more of an SPOP kind of guy. I like S-POP. But tell us a little bit about what this gene is and what it regulates. So, I don't know, Neeraj.

Neeraj Agarwal: Yeah. So SPOP mutation is one of those findings we often see about 10% of cases with prostate cancer, when we order our patient's tissue to go for comprehensive genomic profiling. And what is SPOP? SPOP is a protein. And the way I explain this to my patients is that the job of the protein is to make sure proteins in general do not accumulate in the cells. And whenever SPOP sees proteins accumulating too much, for example, androgen receptor is a protein, it grabs the protein, excessive protein, and put this in the garbage bin of cancer cells, which is proteasome. So it makes sure that protein level remains low, or to the normal extent.

Oliver Sartor: Now, "proteins," that's a really big term. But which proteins are we talking about here that are relevant to prostate?

Neeraj Agarwal: Yes. Androgen receptor.

Oliver Sartor: Androgen receptor.

Neeraj Agarwal: Yeah.

Oliver Sartor: Okay. Androgen receptor. And this is going to be putting it in the garbage can, but it's functioning normally.

Neeraj Agarwal: Yes.

Oliver Sartor: Okay.

Neeraj Agarwal: Exactly. So when SPOP mutation happens, SPOP... So essentially, just to summarize, SPOP's job is to make sure androgen receptor level remains within the normal limits within the prostate cancer cells. Now, when a mutation happens, SPOP cannot really bind well with the androgen receptor. So, it cannot keep the levels down. And androgen receptors start going up in the level. And if I just want to draw an analogy, we can actually see in patients who have SPOP mutation, androgen receptor levels, because they go up, even for the same level of testosterone, the prostate cancer cells, or prostate cells, feel like they're on steroids, because of the high level of androgen receptors.

Oliver Sartor: Dan, what would you like to add to that?

Daniel Petrylak: So ubiquitination is more of a general process that goes on with the proteins. And SPOP has a greater role than just the androgen receptor. There's something called CAPSIN-1, which is a molecule that regulates something called a stress granule. Stress granules are involved in drug resistance, particularly with docetaxel. So SPOP has a broader role, in addition to the androgen receptor, and may also play a role in drug resistance.

Oliver Sartor: Interesting. So, when you're doing your genetic profiling, SPOP is one of the things you're paying attention to. Of course, we paid attention to a lot of other things. If I remember right, and I need a little guidance here, SPOP seems to be exclusive in a number of cells. It seems to be SPOP or other things, it's not SPOP and other things. Is that correct or incorrect? How does it segregate in accordance with other mutations relevant in prostate cancer?

Neeraj Agarwal: So, in the comprehensive genomic profiling series, if you look at, we publish in clinical cancer research and we'll be talking about those data in a moment, SPOP mutation did not seem to be present in the same patients who also had other mutations. So more like an exclusive mutation, if you will, compared to more common, other common NGS findings we see in prostate cancer patients.

Oliver Sartor: SPOP over here, other ones over there.

Neeraj Agarwal: Yeah.

Oliver Sartor: Okay. So, what are the implications about SPOP when you're looking at therapy? What about androgen deprivation? What does it mean for patients getting androgen deprivation? Dan?

Daniel Petrylak: Well, we know that SPOP mutations will predict for a longer response to hormone therapy, particularly with drugs such as abiraterone or just simply ADT alone, Neeraj has published some very, very interesting intriguing data looking at this in terms of those patients who hormone sensitive as to whether they would respond to hormone therapy or not with SPOP mutations. But certainly this is one mechanism of determining whether a patient's going to respond to hormone therapy, and it also may be a mechanism, one of the contributing factors to docetaxel resistance.

Oliver Sartor: Oh, very interesting. Now, what about the ARPIs? Any relationship to the ARPIs?

Neeraj Agarwal: Yeah. So, I'll just build up on what Dan just said. So, we looked at about more than a hundred patients in collaboration with four other institution, and looked at patients who had de novo prostate metastatic prostate cancer. They were diagnosed within like 30 days, and they had NGS testing done within very short period to avoid confounding by prior ADT or any other possible factors which can kick in when you delay these testing for too long. Bottom line is SPOP mutation was associated with much improved response to androgen deprivation therapy alone with a hazard ratio for time to castration resistance or overall survival around 0.4.

Oliver Sartor: That's strong. Quite Strong.

Neeraj Agarwal: Quite strong. But interestingly, this was a patient population without what we call as combination therapy or intensification therapy. They just received single-agent ADT.

Then we actually looked at the Flatiron database. Again, applying those strict parameters, patient had to have de novo metastatic prostate cancer. They could not have received ADT prior, and they had to have genomic sequencing done within literally a few months of diagnosis of prostate cancer. Something very interesting came up. SPOP mutation, in patients who had SPOP mutation, the hazard ratio for time to castration resistance, was 0.2. The hazard ratio for survival was 0.2. This is 80% reduction in risk of progression on death.

Oliver Sartor: That's huge, huge.

Neeraj Agarwal: And this is similar to getting Undetectable PSA level. If you want to look for another similar hazard ratios, which we have seen that, it is for those patients who achieve a PSA level of less than 0.1 nanogram per mL on ADT plus ARPI.

Oliver Sartor: So this is really good news for a patient. If they're diagnosed and you get the SPOP, you can say, "Goodness gracious, you're likely to respond very well to the hormonal therapy and you're even likely to live longer." So that's a powerful message for the patients.

Neeraj Agarwal: Yes, absolutely.

Oliver Sartor: But of course, if you don't do the NGS testing, you never know. So, yet another reason to genetically test those patients in our practice.

Neeraj Agarwal: Yeah. Just practically speaking, if I see a SPOP mutation, obviously I know they're going to respond very well. So, it helps with prognostication and counseling. But taking a step beyond, and Dan will be talking about other mutations and how they interplay with several other things we are seeing in the clinic, but if you just look at a patient with SPOP mutation who is responding very well, I really feel comfortable not seeing the patient every month or every two months. I can actually let them go and not see me for three months. I feel comfortable relying on the PSA levels and not doing CT and bone scans every three months. I'm fine with CT and bone scans every once a year in those patients. So, I think it goes beyond just prognostication.

It also has implications on how I monitor patient. How many times I do scans. And how do we prepare for future? I tell them, "You're going to live longer. You have to be enrolled in exercise program." Or be more vigilant about cardiovascular toxicities because they're going to be living longer, more often than these patients.

Oliver Sartor: That's wonderful. Dan, agree, disagree, add to the discussion?

Daniel Petrylak: Well, I think we need more information. I think this is a great finding. I think that it is something we can use for our patients, but firstly, it does not tell us whether patients should have triplet therapy or doublet therapy. So, one of the things that Neeraj published in that paper was that the hazard ratios were close to one with docetaxel by itself, but it doesn't talk about the combination therapy, and it doesn't really have that structure for the database.

In looking back retrospectively, they could not determine the volume of disease in bone scan, whether they had more than four lesions on bone scan or not. Whether they had visceral metastasis. If you look at the biopsy data, about 60% came from the prostate, only 2% came from the liver. So, that's also looking at a select group of patients.

So I think that it's a great start. It's something we need to confirm prospectively, whether through randomized trials, which are going to be very, very difficult in this day and age, or by using tools such as artificial intelligence. So, a number of years ago, Josep Domingo-Domenech who is now at the Mayo Clinic, Carlos Cordón-Cardó, who is at Mount Sinai, when we were at Columbia, we looked at raising docetaxel-resistant prostate cancer cell lines. And then we looked at the different genetic signatures that we got from that. And it's really varied. You'd lose your epithelial markers. You gain markers of stem cells, such as Notch and GLI.

So not only do we see the emergence of these resistant cells, we see it change, we see this going to the EMT or the epithelial to mesenchymal transition. So, the question is, is this going on in patients? This is where the stress granules come in. Is this more of an effect from those particular stress granules I mentioned with the SPOP mutations? I think that, again, we have to look at this very, very carefully, we have to interrogate the tissue carefully on a prospective basis to understand what's going on.

Oliver Sartor: It's pretty fascinating. We've learned so much. NGS really has not been around that long. We had germline testing, and we implemented that pretty broadly. And we're learning not only about the ability for the homologous recombination repair, we're learning about mismatch repair, we're learning about SPOP, PTEN loss potentially be actionable fairly soon. I mean, all of these changes we learn because we do the testing. I think one of the messages I want to convey here, get the testing done, because the implications of what you find can be large for prognosis and even treatment selection and more.

Daniel Petrylak: Patients want a roadmap. They want to know what their future is. And that's the reason why we do our testing early, because of reasons like SPOP. Identifying DNA repair mutation, looking at the germline so we can counsel the families. I can't emphasize
enough the role of germline testing as well as next-generation sequencing for these patients.

Neeraj Agarwal: And it's unfortunate that most patients are still not getting tested. We recently published in JAMA Network Open using the US-based dataset, which is Flatiron Database, thousands of patients, and is still 2023, only 27% of patients with metastatic prostate cancer had genomic profiling done by NGS testing.

Oliver Sartor: Interesting.

Neeraj Agarwal: Very low number, unacceptable, and I think we need to do a better job.

Oliver Sartor: We have more work to do. But I think discussions like this can highlight the importance and allow individuals who are treating these patients to understand more the implications of the findings that you can get from doing the test. And SPOP is not infrequent. 10%?

Neeraj Agarwal: 10%, yeah.

Oliver Sartor: Yeah. That's a fairly common mutation, and it has implications.

Daniel Petrylak: Yeah. Same as BRCA.

Oliver Sartor: Yeah. Appreciate the conversation. Thank you both.