Tracers Increase PET Imaging Sensitivity in Prostate Cancer

Manoj K. Jain, MD

The emergence of FDA-approved diagnostic tracers such as C-11 choline and F-18 fluciclovine (Axumin) in novel PET imaging modalities for the detection of biochemical recurrence in prostate cancer signals a shift from conventional imaging methods, said Manoj K. Jain, MD.

“The newer imaging tools that we are using are the tracers C-11 choline and F-18 fluciclovine; these are really helpful in visualizing local recurrence as well as metastatic disease with is small,” said Jain. “The sensitivity of these tracers is much higher than conventional imaging methods and they are more specific.”

This increased sensitivity allows the tracers to detect the small lesions and low prostate-specific antigen (PSA) levels in a patient.

In an interview during the 2019 OncLive^® State of the Science Summit™ on Genitourinary Cancers, Jain, Division Chair of Nuclear Medicine Mayo Clinic, discussed these new imaging modalities and what they could mean for the field going forward.

OncLive: What are the drawbacks to traditional imaging modalities and how have they prompted further investigation into more sensitive methods?

Jain: The conventional imaging modalities that have been used in the past for prostate cancer in terms of diagnosis and biochemical recurrence are MRI, CT scan of the body, and bone scans. These modalities have lower sensitivity—especially when the PSA level and the size of the lesions are small. Therefore, we need to look at emerging technologies, especially in molecular imaging, where we are able to detect much smaller lesions and at lower PSA levels. The newer modalities that we are using in PET imaging, that are FDA approved, are the tracers C-11 choline and F-18 fluciclovine.

Do you have a preference with which one you like to use in practice?

Currently, we are using F-18 fluciclovine because C-11 choline is a tracer that has a short half-life and [requires] an onsite cyclotron for the production of the tracer and for use. We are in the process of getting a cyclotron approval at our facility. After that, we will be using C-11 choline, because it will be more readily available to us and we will also be able to schedule patients on any day. The supply of F-18 fluciclovine from the vendor is only on limited days.

Are conventional modalities still being used despite the emergence of these newer imaging modalities? How are you selecting between the two approaches?

The current FDA-approved indication for PET tracers C-11 choline and F-18 fluciclovine are biochemical recurrence of prostate cancer. What is biochemical recurrence? Biochemical recurrence depends on what kind of therapy has been given to the patient for their prostate cancer. If the patient had a prostatectomy, then any rise in PSA level of greater than 0.2 ng/mL is considered abnormal. If the patients had definitive radiation therapy, then any rise of 2 ng/mL from the nadir is considered abnormal. These are the indications for PET imaging at this point in time.

Could you discuss any emerging therapies in the setting of biochemical recurrence?

The new emerging radionuclide for imaging of metastatic prostate cancer is prostate-specific membrane antigen (PSMA)-targeted agents; they can be attached to Gallium-68 or F-18 fluciclovine. Both of those have shown to be more sensitive at a lower PSA level than the current available tracers.

At the end of your presentation at the State of the Science Summit™, you highlighted the success of radioligand therapy. Could you discuss that?

Radioligand therapy for prostate cancer is emerging; it is still investigational in the United States. Radioligand therapy with PSMA is performed using Lutetium-177 PSMA. Lutetium-177 PSMA is attached to the prostate cancer cell’s surface receptor and is internalized, and the radionuclide causes destruction of the cell. This is the upcoming therapy for metastatic disease in patients; it is especially used for smaller lesions because the particle itself travels about 2 mm once it is within the cell. [The therapy] limits the destruction of the normal cell tissue.

What can be anticipated moving forward?

Moving forward, there are several new techniques and tracers that are emerging in the space. The first tracer that we expect to get FDA approved in the near future is a Gallium-68— or F-18–based PSMA tracer. Once it receives approval from the FDA, it would definitely make a difference in terms of patient management, especially in those with lower PSA levels.