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Conversations With Prostate Cancer Experts


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Imaging Metastatic Prostate Cancer

Dr. Eric Rohren is the chair of the department of radiology at Baylor College of Medicine.

Prostatepedia spoke with him about imaging metastatic prostate cancer.

Subscribe to read Dr. Rohren’s comments on radium therapy + imaging. Members can read the interview in their March 2018 issue of Prostatepedia.

In terms of imaging, what kinds of scans can determine if a man has metastases (mets) anywhere in his body?

Dr. Eric Rohren: X-ray has been around for a long time and still has a role to play. It’s easy to obtain, it’s cheap, and it has low radiation exposure. We still rely on a good old-fashioned chest or bone X-ray, depending on the patient’s symptoms.

These days, most patients with any type of malignancy, and specifically prostate cancer, are managed in a couple of ways.

One way is a CAT scan. CAT scan is a 3-D imaging technique that uses X-rays that can take images of the body, chest, abdomen, and pelvis. Most patients with newly diagnosed prostate cancer or treated prostate carcinoma have undergone a CAT scan at some point in the course of their disease. CAT scans can show us the prostate gland, lymph nodes, liver, and many of the different organs where cancer may be hidden.

To supplement that, patients with prostate cancer often get a bone scan, which is a nuclear medicine technique. In a bone scan, we inject radioactive material that goes to the skeleton, and most strongly so in areas where there’s increased skeletal turnover, where something in the bone is inciting a reaction. It may go to benign things like healing fractures, arthritis, and various areas of injury. But the radioactive material also goes to areas of metastatic disease in the skeleton, and it localizes most particularly in those areas, lighting up on these bone scans.

Rather than just a particular region of the body, a bone scan shows us from the top of the head all the way down to the feet, which is nice. We get a look at the entire skeleton, and we can look for the little spots that are lighting up that may indicate the presence of metastatic disease in the skeleton.

CAT scans and bone scans are very widely used. A bone scan is a little bit better than a CAT scan in looking for these bone metastases, so the two really augment each other in detection of the disease.

Beyond these, we do have some newer imaging techniques coming into play. There’s a way of doing a bone scan with PET scanner. A PET scanner is another nuclear medicine technique that is more sensitive than a standard nuclear medicine camera, and it acquires a CAT scan at the same time. You can look at the images on the nuclear medicine technique overlaid on the CT scan to see where exactly the activity is and what it’s due to.

We can also use some agents with PET scanning to look at the skeleton. A so-called fluoride PET/CT bone scan seems to have many advantages over a conventional bone scan in terms of detecting smaller disease, more sites of disease, and things like that. MRI is also used in some cases.

Traditionally, MRI is used to evaluate specific areas, so if there’s pain in a particular area such as the skeleton,

MRI is a great way to do that. MRI is also used to look directly at the prostate gland and at the prostate bed after prostate surgery or after other therapy in the pelvis. It can be very good at detecting small volumes of disease. The problem with PET scanning and MRI scanning is that they are less accessible, although MRI is in most places now, and most major areas have access to a PET scanner.

Then there’s the issue of cost. Both techniques are costly. We need to determine if the added cost is justified by the additional information that those scans provide.

Beyond these techniques, the exciting thing for nuclear medicine is the new developments on the horizon. As we discover more about the molecular nature of disease, why cancer forms, and what makes and defines a cancer cell, those molecular discoveries can be translated into imaging studies that we can then use with PET scanning to be even more sensitive for detection of disease.

For example, there are several new molecular tracers in the United States that are approved for imaging of prostate cancer. Choline and Axumin (FACBC) are both agents approved in the United States for use with PET/CT.

Internationally, people are moving to a compound called prostate surface membrane antigen (PSMA) that can image prostate carcinoma. It seems to be even better than Choline or Axumin. The data is still a little bit undetermined at this point, but there’s a lot of excitement around these newer agents being able to seek out cancer in very small volumes anywhere it occurs in the body.

Then I guess the question becomes: when do you treat?

Dr. Rohren: Yes. That is very much the question. As we discover more and more sites of disease and smaller sites of disease, the question becomes: do we need to treat those aggressively or conservatively? We’re discovering new things about tumor biology, and we need to understand how that gets translated into the best appropriate therapy for patients.

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What Comes After MRI?

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Dr. Matthew Cooperberg is an Associate Professor of Urology and the Helen Diller Family Chair in Urology at the University of California, San Francisco. He is keenly interested in risk-stratifying prostate cancer to better match treatments to those most likely to benefit.

Prostatepedia spoke with Dr. Cooperberg recently about the role imaging plays in prostate cancer treatment.

Are there any other imaging techniques on the horizon that may replace the MRI?

Dr. Cooperberg: There is a lot of excitement for what will be the next-generation MR spectroscopy based on hyperpolarized Carbon-13 imaging. This is next-generation MR imaging in which we can essentially watch metabolic pathways unfold in real time at the millimeter level. That’s going to be incredible. This technology was developed by John Kurhanewicz at UCSF and is in late phase testing now. A few of these machines exist so far around the world; this may really be a game changer.

Technologies for next-generation ultrasound may also be able to yield a very high-resolution picture. These technologies have to be studied carefully head-to-head. It may bear out that better ultrasound technology will prove more cost-effective and easier on the patient than MRI, which requires separate visits, separate costs, and multiple physicians. Plus, MR is competing—especially when we talk about active surveillance—with blood, urine, and tissue biomarkers. Should a surveillance candidate who is on the edge get an MRI, a Decipher test, or both?

Would you use multiple tools or just one?

Dr. Cooperberg: Potentially multiple, but if everyone uses multiple tools, the cost increases exponentially. We don’t always know what to do with conflicting information. If you have a reassuring MRI and a concerning Decipher score, what do you do? If you have a high biomarker score and the MRI still doesn’t show anything, what do you do? These are challenging questions.

From a research standpoint, this is what makes it fun. But for the man on the ground, there is a lot of confusion. It’s part of the reason that I’m skeptical about how aggressively a number of these tests are marketed in the prostate cancer community.

You mean how tests like Decipher are marketed in the community?

Dr. Cooperberg: And MRI. It’s all in the same category. When I give a talk on MRI, I consider it to be a novel biomarker. It faces all the same challenges and has to play by all the same rules as Polaris or Decipher. You’ve got to prove that it’s going to give you better information than you can get from the basic clinical assessment. You’ve got to prove it’s going to help you make a better decision. And you’ve got to prove that it gets better outcomes, just like the biomarkers. Just as we’re not quite there with the biomarkers, we’re not quite there with MRI.

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PET/CT Imaging + Radiation?

 

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Dr. Michael Zelefsky, a radiation oncologist, is Professor of Radiation Oncology, Chief of the Brachytherapy Service, and Co-Leader of the Genitourinary Disease Management Team at Memorial Sloan Kettering Cancer Center in New York City.

Prostatepedia recently spoke with him about how advances in imaging have impacted radiation therapy. Subscribe to read the entire conversation.

Do you think molecular imaging will be incorporated soon?

Dr. Zelefsky: There’s a lot of excitement with PET/CT imaging. PET imaging fused with MRI is also emerging now. This has been used effectively for various disease sites, not only prostate cancer. For prostate cancers specifically, newer PET tracers such as PET C-11 Choline and exciting developments in PSMA tracers will be used. These provide us unique opportunities to see where micrometastatic disease could be lodged. That information is critical for the radiation oncologist to pinpoint the disease. There are also exciting developments using some of these tracers as a form of therapy. Tracers such as PSMA are linked to lutetium-177 and tracers can be integrated with radiation planning as well. We are on the verge of seeing these new developments; these changes will soon be integrated with radiation.

Is there anything else you think patients should know about imaging’s role in radiation therapy?

Dr. Zelefsky: With new advances in imaging and by working in close collaboration with diagnostic radiology, we are getting much more accurate information concerning where microscopic disease is located and the critical zones within the prostate where tumors are lodged. We use imaging to consider re-biopsying patients where there may be a discrepancy between what looks like earlier states of disease, but the MRI shows there is greater volume of disease than what was anticipated. We need to know this information in order to plan the radiation well. We need to consider opportunities to intensify the dose to the DIL in the prostate and whether there is nodal disease and where exactly the nodal disease could be within the pelvis. Imaging plays a huge role in our follow-up with patients, allowing us to detect recurrences earlier than ever before. This is vital information for patients because earlier detection of recurrences allow for salvage therapies much sooner and treating such patients at earlier time points is often associated with more successful outcomes.

In the future, imaging will help us consider focal ablative therapies where the paradigm is shifting in earlier cancer s. Simply put, we could just focus on the DIL and spare the rest of the prostate if we can be sure that there is no significant disease in other parts of the gland. There have been a number of efforts to use focal therapy with advanced imaging to small subunits of the prostate. So new imaging possibilities are opening up new directions and opportunities in the treatment of prostate cancer.

Subscribe to read the rest of the conversation on imaging + radiation therapy.