PCa Commentary | Volume 156 – August 2021
Posted by Edward Weber | August 2021
PYLARIFY — A New PET Imaging Agent for Staging Primary Prostate Cancer and Recurrence
“Pylarify” is a recently FDA-approved tracer for imaging the prostate specific membrane antigen (PSMA) displayed on ~95% of prostate cancer cells. This urea-based radiotracer combines the small molecule DCFPyL, a PSMA targeting agent, with the positron-emitting isotope fluorine F-18, facilitating PET imaging of PSMA-expressing prostate cancer cells. In general design, it is very similar to the well-researched 68Gallium-PSMA PET/CT and has comparable sensitives.
The FDA approval of Pylarify permits PET imaging in biopsy-diagnosed unfavorable intermediate-risk and high-risk cancer (D’Amico definition) prior to definitive initial therapy, and also in relapsed cancer.
The approval was based on favorable results of two large clinical trials, OSPREY and CONDOR, both of which compared the safety and performance of 18F-DCFPyL to conventional imaging with CT and technetium bone scanning. In both studies, the specificity for cancer detection in pretreatment staging and at recurrence was significantly superior.
The forthcoming availability of 18F-DCFPyL will likely have a profound impact on the initial management of men newly diagnosed with advanced prostate cancer. Unlike the 68Ga-PSMA PET/CT, which is only FDA-approved at UCLA and UCSF for initial diagnosis, Lantheus Holdings, Inc., will likely make Pylarify nationally available. The manufacture of 68Ga requires a special generator, but the F-18 agent can be made at local manufacturing sites and be provided to nearby nuclear medicine facilities, similar to the acquisition of the Axumin and F18-FDG tracers.
A pre-treatment Pylarify PET/CT has the potential to change management plans based on conventional imaging
In the OSPREY trial, the Pylarify PET/CT detected metastatic disease in 58% (19 of 33) of men with advanced cancer who were negative for metastases on conventional CT and bone scanning. The men in this study had been scheduled to undergo radical prostatectomy and lymph node dissection. The metastatic disease was confirmed pre-op by extra-pelvic biopsies in 10 of 11 men.
Additionally, 82 men in the study had been considered to have metastatic spread on conventional imaging, but a Pylarify PET/CT downstaged 22% (18 of 82) of men, concluding that they were metastases free.
The OSPREY data is similar to the multiple studies reporting that a pre-initial therapy 68Ga PET/CT in men with advanced disease changes management plans in 50-60% of men. Changes might include extending the field of planned surgery or radiation to include the newly-found disease, metastases-directed therapy (e.g., with CyberKnife) + ADT combined with treatment of the primary, or offering only androgen deprivation therapy.
Considering the 98% specificity of the Pylarify PET/CT compared to conventional imaging’s 67%, the use of conventional imaging would likely be avoided.
The Performance of the Pylarify PET/CT at disease recurrence following primary local therapy
Choyke et al (Journal of Nuclear Medicine, June 2020) addressed this in a prospective study of 18F-DCFPyL PET/CT in 90 men with biochemical recurrence with a median PSA of 2.5 ng/mL (range 0.21-35.5). The men were negative on conventional imaging. “The PSMA PET lesion detection rate correlated with PSA, PSA kinetics, and the original primary tumor grade.” No man had had ADT.
The detection rate was 47.6% at PSA >0.2 to <0.5 ng/mL; 50% at 0.5 to 1.0; 88.9% at 1 to <2.0; and 94% at PSA values above 2.0 ng/mL. Tumor recurrence was histologically confirmed in 40% of men.
Their conclusion: the detection rate of recurrent disease of nearly 50% in patients with PSA values less than 0.5 ng/ml could “substantially impact clinical management.”
BOTTOM LINE:
The FDA approval for Pylarify PET/CT for use prior to initial primary therapy for men with advanced prostate cancer will likely have a significant impact on the management of these men.
Your comments and requests for information on a specific topic are welcome e-mail ecweber@nwlink.com.
Please also visit https://prostatecancerfree.org/prostate-cancer-news for a selection of past issues of the PCa Commentary covering a variety of topics.
“I want to thank Dawn Scott, Staffperson, Tumor Institute Radiation Oncology Group, and Mike Scully, Librarian, Swedish Medical Center, for their unfailing, timely, and resourceful support of the Commentary project. Without their help this Commentary would not be possible.”
ABOUT THE AUTHOR
Edward Weber, MD, is a retired medical oncologist living in Seattle, Washington. He was born and raised in a suburb of Reading, Pennsylvania. After graduating from Princeton University in 1956 with a BA in History, Dr. Weber attended medical school at the University of Pennsylvania. His internship training took place at the University of Vermont in Burlington.
A tour of service as a Naval Flight Surgeon positioned him on Whidbey Island, Washington, and this introduction to the Pacific Northwest ultimately proved irresistible. Following naval service, he received postgraduate training in internal medicine in Philadelphia at the Pennsylvania Hospital and then pursued a fellowship in hematology and oncology at the University of Washington.
His career in medical oncology was at the Tumor Institute of the Swedish Hospital in Seattle where his practice focused largely on the treatment of patients experiencing lung, breast, colon, and genitourinary cancer and malignant lymphoma.
Toward the end of his career, he developed a particular concentration on the treatment of prostate cancer. Since retirement in 2002, he has authored the PCa Commentary, published by the Prostate Cancer Treatment Research Foundation, an analysis of new developments in the prostate cancer field with essays discussing and evaluating treatment management options in this disease. He is a regular speaker at various prostate cancer support groups around Seattle.
