The Importance of Genetic Testing for Prostate Cancer

In this episode of ASCO Educational podcasts, we'll explore how we interpret and integrate recently reported clinical research into practice. The first scenario involves a 72-year old man with high-risk, localized prostate cancer progressing to hormone-sensitive metastatic disease. 

Our guests are Dr. Kriti Mittal (UMass Chan Medical School) and Dr. Jorge Garcia (Case Western Reserve University School of Medicine). Together they present the patient scenario (1:12), review research evidence regarding systemic and radiation therapy for high-risk localized disease (5:45), and reflect on the importance of genetic testing and (10:57) and considerations for treatment approaches at progression to metastatic disease (16:13). 

Speaker Disclosures Dr. Kriti Mittal:  Honoraria – IntrinsiQ; Targeted Oncology; Medpage; Aptitude Health; Cardinal Health  Consulting or Advisory Role – Bayer; Aveo; Dendreon; Myovant; Fletcher; Curio Science; AVEO; Janssen; Dedham Group  Research Funding - Pfizer

Dr. Jorge Garcia:  Honoraria - MJH Associates: Aptitude Health; Janssen Consulting or Advisor – Eisai; Targeted Oncology Research Funding – Merck; Pfizer; Orion Pharma GmbH; Janssen Oncology;  Genentech/Roche; Lilly  Other Relationship - FDA

Resources  ASCO Article: Implementation of Germline Testing for Prostate Cancer: Philadelphia Prostate Cancer Consensus Conference 2019

ASCO Course: How Do I Integrate Metastasis-directed Therapy in Patients with Oligometastatic Prostate Cancer? (Free to Full and Allied ASCO Members)

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TRANSCRIPT

Dr. Kriti Mittal: Hello and welcome to this episode of the ASCO Education Podcast. Today we'll explore how we interpret and integrate recently reported clinical research into practice, focusing on two clinical scenarios: localized prostate cancer progressing to hormone-sensitive metastatic disease; and a case of de novo metastatic hormone-sensitive prostate cancer progressing to castration-resistant disease.

My name is Kriti Mittal and I am the Medical Director of GU Oncology at the University of Massachusetts. I am delighted to co-host today's discussion with my colleague, Dr. Jorge Garcia. Dr. Garcia is a Professor of Medicine and Urology at Case Western Reserve University School of Medicine. He is also the George and Edith Richmond Distinguished Scientist chair and the current chair of the Solid Tumor Oncology Division at University Hospital's Seidman Cancer Center. Let me begin by presenting the first patient scenario. 

Case 1: A 72-year-old male was referred to urology for evaluation of hematuria. A rectal exam revealed an enlarged prostate without any nodules. A CT urogram was performed that revealed an enlarged prostate with bladder trabeculations. A cystoscopy revealed no stones or tumors in the bladder, but the prostatic urethra appeared to be abnormal looking. Transurethral resection of the prostate was performed. The pathology revealed Gleason score 4+5=9 prostate cancer, involving 90% of the submitted tissue. PSA was performed one week later and was elevated at 50. Patient declined the option of radical prostatectomy and was referred to radiation and medical oncology.  

So I guess the question at this point is, Dr. Garcia, in 2023, how do you stage patients with high-risk localized prostate cancer and how would you approach this case?

Dr. Jorge Garcia: That's a great question and a great case, by the way, sort of what you and I in our practice will call ‘bread and butter’. Patients like this type of case that you just presented come from different places to our practice.  So either they come through urology or oftentimes they may come through radiation oncology. And certainly, it depends where you practice in the United States, at ‘X’, US, they may come through medical oncology.  

So I think that the first question that I have is in whatever role I'm playing in this case, where the patient has seen a urologist or a rad onc or me first, I think it's important for us in medical oncology, at least in the prostate cancer space, to talk about how do we think of their case and put those comments into context for the patient. It's very simple for you to tell a patient you can probably have surgery, radiation therapy, but at the end of the day, how do you counsel that patient as to the implications of the features of his disease is going to be really important. I use very simple examples that I relate to my patients, but really this patient is a patient that has very high-risk prostate cancer based upon the NCCN guidelines and how we actually stratify patients into what we call low-risk, intermediate-, and high-risk, and between those very low and very high risk. 

So his PSA is high, very high, I would argue. His Gleason score, now, what we call group grading is high. He has high-volume disease. So the first question that I would have is, what are the choices for treatment for a patient like this? But even before you and I may talk about treatment options, we really want to understand the volume of their disease and whether or not they have localized prostate cancer with high-risk features or whether or not they have locally advanced or hopefully not metastatic disease. So back in the days prior to the FDA approval for PSMA PET imaging, we probably will have a Technetium-99 whole-body bone scan, and/or we probably will actually use CT scanning. Most people in the past, we used to do just a CT of the abdomen and pelvic region. As you know, with the movement of oral agents in the advanced setting, I think most of us will do a chest CT, abdomen and pelvic region, and certainly we also probably will have a Technetium-99 bone scan. 

Now, with the utility and the use of PET imaging, I think most people like him will probably undergo PET PSMA, where you use F-18 PSMA or Gallium-68 PSMA. I think the importance depends on how you look at the approval of these two technologies. I think that PET PSMA imaging is here to stay. It's probably what most of us will use. And based upon that, we will define yet the truest stage of this patient. So right now, what we know is he has high-risk features. Hopefully, their disease is localized. We'll probably put the patient through an imaging technology. If you don't have access to a PET, then obviously CT and a bone scan will do. But if you do, the PET will actually help us define if the patient has disease outside of the prostate region, in the pelvic area, or even if they have distant metastases.

Dr. Kriti Mittal: I would agree with that approach, Dr. Garcia. I think in the United States, we've been late adopters of PSMA scans. I think this patient with high-risk localized disease, if insurance allows at our institution, would get a PSMA for staging. There are still some patients where insurance companies, despite peer-to-peer evaluations, are not approving PSMAs. And in those situations, the patient would benefit from conventional CTs and a bone scan. So let's say this patient had a PSMA and was found not to have any regional or distant metastases. He decided against surgery, and he is seeing you as his medical oncologist together with radiation. What would your recommendations be? 

Dr. Jorge Garcia: I think the bigger question is, do we have any data to suggest or to demonstrate that if in the absence of metastatic disease with conventional imaging or with emerging technologies such as PSMA PET, there is no evidence of distant disease, which I think you probably agree with me, that would be sort of unlikely with a patient with these features not to have some form of PSMA uptake somewhere in their body. But let's assume that indeed then the PSMA PET was negative, so we're really talking about high-risk localized prostate cancer. So I don't think we can tell a patient that radical prostatectomy would not be a standard of care. We never had a randomized trial comparing surgery against radiation therapy. This patient has already made that decision and surgery is not an option for him. If he, indeed, had elected radiotherapy, the three bigger questions that I ask myself are where are you going to aim the beam of that radiation therapy? What technology, dose, and fractionation are you going to use? And lastly, what sort of systemic therapy do you need, if any, for that matter? Where we do have some data maybe less controversial today in 2023 compared to the past? But I think the question is, do we do radiation to the prostate only or do we expand the field of that radiation to include the pelvic nodes? 

Secondly, do we use IMRT? Do you use proton beam or not? Again, that's a big question that I think that opens up significant discussions. But more important, in my opinion, is the term of hypofractionation. I think the field of radiation oncology has shifted away from the old standard, five, seven weeks of radiation therapy to more hypofractionation, which in simple terms means a higher dose over a short period of time. And there was a concern in the past that when you give more radiation on a short period of time, toxicities or side effects would increase. And I think that there is plenty of data right now, very elegant data, demonstrated that hypofractionation is not worse with regards to side effects. I think most of us will be doing or supporting hypofractionation. And perhaps even to stretch that, the question now is of SBRT. Can we offer SBRT to a selected group of patients with high-risk prostate cancer? And again, those are discussions that we will naturally, I assume, in your practice, in your group, you probably also have along with radiation oncology. 

Now, the bigger question, which in my mind is really not debatable today in the United States, is the need for systemic therapy. And I think we all will go back to the old data from the European EORTC data looking at the duration of androgen deprivation therapy. And I think most of us would suggest that at the very least, 24 months of androgen deprivation therapy is the standard of care for men with high-risk prostate cancer who elect to have local definitive radiation therapy as their modality of treatment. I think that whether or not it's 24 or 36, I think that the Canadian data looking at 18 months didn't hit the mark. But I think the radiation oncology community in the prostate cancer space probably has agreed that 24 months clinically is the right sort of the sweetest spot. 

What I think is a bit different right now is whether or not these patients need treatment intensification. And we have now very elegant data from the British group and also from the French group, suggesting, in fact, that patients with very high-risk prostate cancer who don't have evidence of objective metastasis may, in fact, benefit from ADT plus one of the novel hormonal agents, in this case, the use of an adrenal biosynthesis inhibitor such as abiraterone acetate. So I think in my practice, what I would counsel this patient is to probably embark on radiotherapy as local definitive therapy and also to consider 24 months of androgen deprivation therapy. But I would, based upon his Gleason score of group grading, his high-volume disease in the prostate gland, and his PSA, to probably consider the use of the addition of abiraterone in that context.

Dr. Kriti Mittal: That is in fact how this patient was offered treatment. The patient decided to proceed with radiation therapy with two years of androgen deprivation. And based on data from the multi-arm STAMPEDE platform, the patient met two of the following three high-risk features Gleason score >8, PSA >40, and clinical >T3 disease. He was offered two years of abiraterone therapy. Unfortunately, the patient chose to decline upfront intensification of therapy. In addition, given the diagnosis of high-risk localized prostate cancer, the patient was also referred to genetic counseling based on the current Philadelphia Consensus Conference guidelines. Germline testing should be considered in patients with high-risk localized node-positive or metastatic prostate cancer, regardless of their family history. In addition, patients with intermediate-risk prostate cancer who have cribriform histology should also consider germline genetic testing. 

Access to genetic counseling remains a challenge at several sites across the US, including ours. There is a growing need to educate urologists and medical oncologists to make them feel comfortable administering pretest counseling themselves and potentially ordering the test while waiting for the results and then referring patients who are found to have abnormalities for a formal genetics evaluation. In fact, the Philadelphia Consensus Conference Guideline offers a very elegant framework to help implement this workflow paradigm in clinical practice. And at our site, one of our fellows is actually using this as a research project so that patients don't have to wait months to be seen by genetics. This will have implications, as we will see later in this podcast, not only for this individual patient as we talk about the role of PARP inhibitors but also has implications for cascade testing and preventative cancer screening in the next of kin.

Dr. Jorge Garcia: Dr. Mittal, I think that we cannot stress enough the importance of genetic testing for these patients. Oftentimes I think one of the challenges that our patients are facing is how they come into the system. If you come through urology, especially in the community side, what I have heard is that there are challenges trying to get to that genetic counsel. Not so much because you cannot do the test, but rather the interpretation of the testing and the downstream effect as you're describing the consequences of having a positive test and how you're going to counsel that patient. If you disregard the potential of you having an active agent based upon your genomic alteration, is the downstream of how your family may be impacted by a finding such as the DNA repair deficiency or something of that nature. So for us at major academic institutions because the flow how those patients come through us, and certainly the bigger utilization of multi-disciplinary clinics where we actually have more proximity with radiation oncology urology, and we actually maybe finesse those cases through the three teams more often than not, at least discuss them, then I think that's less likely to occur. But I think the bigger question is the timing of when we do testing and how we do it. 

So there are two ways -- and I'd love to hear how you do it at your institution -- because there are two ways that I can think one can do that. The low-hanging fruit is you have tissue material from the biopsy specimen. So what you do, you actually use any of the commercial platforms to do genomic or next-generation sequencing or you can do in-house sequencing if your facility has an in-house lab that can do testing. And that only gets you to what we call ‘somatic testing’, which is really epigenetic changes over time that are only found in abnormal cells. It may not tell you the entire story of that patient because you may be missing the potential of identifying a germline finding. So when you do that, did you do germline testing at the same time that you do somatic testing or did you start with one and then you send to genetic counseling and then they define who gets germline testing?

Dr. Kriti Mittal: So at our site, we start with germline genetic testing. We use either blood testing or a cheek swab assay and we send the full 84-gene multigene panel.

Dr. Jorge Garcia: Yeah, and I think for our audience, Dr. Mittal, that's great. I don't think you and I will be too draconian deciding which platform one uses. It's just that we want to make sure that at least you test those patients. And I think the importance of this is if you look at the New England Journal paper from many years ago, from the Pritchard data looking at the incidence of DNA repair deficiency in men with prostate cancer in North America, that was about what,  around 10% or so, take it or leave it. So if you were to look only for germline testing, you only will, in theory, capture around 10% of patients. But if you add somatic changes that are also impacting the DNA pathway, then you may add around 23%, 25% of patients. So we really are talking that if we only do one type of testing, we may be missing a significant proportion of patients who still may be candidates, maybe not for family counseling if you had a somatic change, rather than germline testing, the positivity, but if you do have somatic, then you can add into that equation the potential for that patient to embark on PARP inhibitors down the road as you stated earlier. It may not change how we think of the patient today, or the treatment for that matter. But you may allow to counsel that patient differently and may allow to sequence your treatments in a different way based upon the findings that you have. So I could not stress the importance of the NCCN guidelines and the importance of doing genetic testing for pretty much the vast majority of our patients with prostate cancer.

Dr. Kriti Mittal: Going back to our patient, three years after completion of his therapy, the patient was noted to have a rising PSA. On surveillance testing, his PSA rose from 0.05 a few months prior to 12.2 at the time of his medical oncology appointment. He was also noted to have worsening low back pain. A PSMA scan was performed that was noteworthy for innumerable intensely PSMA avid osseous lesions throughout his axial and appendicular skeleton. The largest lesion involved the right acetabulum and the right ischium. Multiple additional sizable lesions were seen throughout the pelvis and spine without any evidence of pathologic fractures. So the question is, what do we do next?

Dr. Jorge Garcia: The first question that I would have is, the patient completed ADT, right? So the patient did not have treatment intensification, but at the very least he got at least systemic therapy based upon the EORTC data. And therefore, one would predict that his outcome will have been improved compared to those patients who receive either no ADT or less time on ADT. But what I'm interested in understanding is his nadir PSA matters to me while he was on radiation and ADT. I would like to know if his nadir PSA was undetectable, that's one thing. If he was unable to achieve an undetectable PSA nadir, that would be a different thought process for me.  

And secondly, before I can comment, I would like to know if you have access to his testosterone level. Because notably, what happens to patients like this maybe is that you will drive down testosterone while you get ADT, PSAs become undetectable. Any of us could assume that the undetectability is the result of the radiation therapy. But the true benefit of the combination of radiation and ADT in that context really comes to be seen when the patient has got off the ADT, has recovered testosterone, and only when your testosterone has normalized or is not castrated, then we'll know what happens with your serologic changes. If you rise your PSA while you recover testosterone, that is one makeup of patient. But if you rise your PSA while you have a testosterone at the castrated level, that would be a different makeup of a patient. So do we have a sense as to when the patient recovered testosterone and whether or not if his PSA rose after recovery? 

Dr. Kriti Mittal: At the time his PSA rose to 12, his testosterone was 275.

Dr. Jorge Garcia: Okay, perfect. You and I would call this patient castration-naive or castration-sensitive. I know that it's semantics. A lot of people struggle with the castration-naive and castration-sensitive state. What that means really to me, castration-naive is not necessarily that you have not seen ADT before. It's just that your cancer progression is dependent on the primary fuel that is feeding prostate cancer, in this case, testosterone or dihydrotestosterone, which is the active metabolite of testosterone. So in this case, recognizing the patient had a testosterone recovery and his biochemical recurrence, which is the rising of his PSA occur when you have recovery of testosterone, makes this patient castration-sensitive. Now the PET scan demonstrates now progression of his disease. So clearly he has a serologic progression, he has radiographic progression. I assume that the patient may have no symptoms, right, from his disease? 

Dr. Kriti Mittal: This patient had some low back pain at the time of this visit. So I think we can conclude he has clinical progression as well.

Dr. Jorge Garcia: Okay, so he had the triple progression, serologic, clinical, and radiographic progression. The first order of business for me would be to understand the volume of his disease and whether we use the US CHAARTED definition of high volume or low volume, or whether we use the French definition for high volume from Latitude, or whether we use STAMPEDE variation for definition, it does appear to me that this patient does have high-volume disease. Why? If you follow the French, it's a Gleason score of >8, more than three bone metastases, and the presence of visceral disease, and you need to have two out of the three. If you follow CHAARTED definition, we did not use Gleason scoring, the US definition. We only use either the presence of visceral metastases or the presence of more than four bone lesions, two of which had to be outside the appendicular skeleton. So if we were to follow either/or, this patient would be high-volume in nature. 

So the standard of care for someone with metastatic disease, regardless of volume, is treatment intensification, is you suppress testosterone with androgen deprivation therapy. And in this case, I'd love to hear how you do it in Massachusetts, but here, for the most part, I would actually use a GnRH agonist-based approach, any of the agents that we have. Having said that, I think there is a role to do GnRH antagonist-based therapy. In this case, degarelix, or the oral GnRH antagonist, relugolix, is easier to get patients on a three-month injection or six-month injection with GnRH agonist than what it is on a monthly basis. But I think it's also fair for our audience to realize that there is data suggesting that perhaps degarelix can render testosterone at a lower level, meaning that you can castrate even further or have very low levels of testosterone contrary to GnRH agonist-based approaches. 

And also for patients maybe like this patient that you're describing, you can minimize the flare that possibly you could get with a GnRH agonist by transiently raising the DHT before the hypothalamic-pituitary axis would shut it down. So either/or would be fine with me. Relugolix, as you know, the attraction of relugolix for us right now, based upon the HERO data, is that you may have possibly less cardiovascular side effects. My rationale not to use a lot of relugolix when I need treatment intensification is quite simple. I'm not aware, I don't know if you can mitigate or minimize that potential cardiovascular benefit by adding abiraterone or adding one of the ARIs, because ARIs and abiraterone by themselves also have cardiovascular side effects. But either/or would be fine with me. The goal of the game is to suppress your male hormone. 

But very important is that regardless of volume, high or low, every patient with metastatic disease requires treatment intensification. You can do an adrenal biosynthesis inhibitor such as abiraterone acetate. You can pick an androgen receptor inhibitor such as apalutamide or enzalutamide if that's the case. The subtleties in how people feel comfortable using these agents, I think, none of us – as you know, Dr. Mittal - can comment that one oral agent is better than the other one. Independently, each of these three oral agents have randomized level 1, phase III data demonstrating survival improvement when you do treatment intensification with each respective agent. But we don't have, obviously, head-to-head data looking at this. 

What I think is different right now, as you know, is the data with the ARASENS data, which was a randomized phase III trial, an international effort looking at triple therapy, and that is male hormone suppression plus docetaxel-based chemotherapy against testosterone suppression plus docetaxel-based chemotherapy plus the novel androgen receptor inhibitor known as darolutamide. This trial demonstrated an outcome survival improvement when you do triple therapy for those high-volume patients. And therefore, what I can tell you in my personal opinion and when I define a patient of mine who is in need of chemotherapy, then the standard of care in my practice will be triple therapy. So if I know you are a candidate for chemotherapy, however, I make that decision that I want you to get on docetaxel upfront. If you have high-volume features, then the standard of care would not be ADT and chemo alone, it would be ADT, chemo, and darolutamide. 

What I don't know, and what we don't know, as you know, is whether or not triple therapy for a high-volume patient is better, the same, equivalent, or less than giving someone ADT plus a novel hormonal agent. That is the data that we don't have. There are some meta-analyses looking at the data, but I can tell you that at the very least, if you prefer chemo, it should be triple therapy. If you prefer an oral agent, it certainly should be either apalutamide, abiraterone acetate, and/or enzalutamide. But either/or, patients do need treatment intensification, and what is perplexing to me, and I know for you as well, is that a significant proportion of our patients in North America are still not getting treatment intensification, which is really sub-optimal and sub-standard for our practice. 

Dr. Kriti Mittal: Thank you, Dr. Garcia, for a terrific discussion on the application of recent advances in prostate cancer to clinical practice. In an upcoming podcast, we will continue that discussion exploring management of de novo metastatic prostate cancer.  

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