Staying On-Target

As a cancer becomes more aggressive, it can gain the ability to spread to other parts of the body. When this happens, it becomes harder to treat using targeted treatments, such as surgical removal and radiotherapy.

However, a recent study from Princess Margaret Cancer Centre aimed to expand the opportunities for curing the disease by unveiling a new gray zone for prostate cancer patients—a state in which the cancer has begun to spread but can still be targeted.

Cells from the prostate have a specific molecule on their surfaces called Prostate Specific Membrane Antigen (PSMA). When cancer forms in the prostate, the resulting cancer cells also have PSMA on their surfaces. This molecule can be targeted using an imaging agent and visualized using positron emission tomography (PET). This approach can be used to find prostate cancer cells, even if they have spread to other parts of the body.

UHN has developed the ability to produce this imaging agent locally through CanProbe—a joint initiative between UHN and the Centre for Probe Development and Commercialization—which provides access to specialized expertise and facilities for the development of new radiopharmaceuticals.

A team led by Techna Affiliate Scientist Dr. Alejandro Berlin was the first to apply this novel technology at UHN through a clinical trial involving 87 prostate cancer patients whose disease had returned. The conventional treatments aimed at curing these patients had been exhausted—and after prostate cancer returns and has spread, oncologists typically can no longer use targeted therapies. Instead, they resort to chemotherapy or hormone therapy—treatments that can control the disease for prolonged intervals but have little hope of eradicating the cancer.

The study aimed to use the advanced imaging approach to better identify the degree of prostate cancer spread and to see whether some of these patients could still benefit from targeted treatment.

Using the PSMA-PET method, the team found that 71% of patients had limited spread of cancer cells—which they termed “oligorecurrent disease”—versus just 22% with widespread disease. The trial then used the imaging results showing precisely where the cancer had spread so that radiation therapy or surgery could be used.

The targeted treatments were able to control the cancer in a majority of patients, and were able to completely remove the evidence of cancer in about one in five patients.

This study not only adds to the emerging evidence demonstrating the value of the PSMA imaging in the management prostate cancer, but it also expands the potential use of curative treatments—particularly for those with a limited degree of spread (i.e., oligorecurrent cancer). The research team is now helping to advance larger international trials that will determine further individualized treatment strategies.

“This was a collaborative effort between the genitourinary site group at the Princess Margaret Cancer Centre and the Joint Department of Medical Imaging under the auspices and vision established by the Techna Institute. By enabling us to apply these cutting-edge approaches, this study has benefited and continues to benefit our patients,” concludes Dr. Berlin.

This work was supported by the Terry Fox Research Institute, Abbvie CARO Uro-Oncologic Radiation Awards, the Astellas Prostate Cancer Innovation Fund, the University of Toronto and The Princess Margaret Cancer Foundation.

Glicksman RM, Metser U, Vines D, Valliant J, Liu Z, Chung PW, Bristow RG, Finelli A, Hamilton R, Fleshner NE, Perlis N, Zlotta AR, Green D, Bayley A, Helou J, Raman S, Kulkarni G, Catton C, Lam T, Chan R, Warde P, Gospodarowicz M, Jaffray DA, Berlin A. Curative-intent Metastasis-directed Therapies for Molecularly-defined Oligorecurrent Prostate Cancer: A Prospective Phase II Trial Testing the Oligometastasis Hypothesis. Eur Urol. 2021 Mar 5 DOI: 10.1016/j.eururo.2021.02.031