PSMA PET Imaging Pinpoints Most Pelvic Nodal Metastases in High-Risk Prostate Cancer

NEW YORK (Reuters Health) – Diagnostic imaging with 68Ga-PSMA-11 PET detects about 80% of pelvic nodal metastases at initial staging of intermediate to high-risk prostate cancer, but a negative scan does not rule out the need for dissection, researchers say.

“We were expecting to have a higher sensitivity for pelvic disease than the study found, and this highlights how difficult it is to detect very small metastases in prostate cancer patients,” Dr. Thomas Hope of the University of California, San Francisco told Reuters Health by email.

Prostate-specific membrane antigen (PSMA) PET “is clearly the best way to stage patients with prostate cancer, but can miss low-volume disease in patients at initial staging,” he said.

As reported in JAMA Oncology, Dr. Hope and colleagues enrolled 764 men (median age, 69) with intermediate- to high-risk prostate cancer considered for prostatectomy in a multicenter single-arm open-label phase 3 imaging trial.

The primary end point was the sensitivity and specificity of 68Ga-PSMA-11 PET imaging for the detection pelvic lymph nodes versus histopathology on a per-patient basis, using nodal region correlation.

Of the men who underwent imaging for primary staging, and 277 (36%) subsequently underwent prostatectomy with lymph node dissection, and they comprised the efficacy analysis cohort.

Pathology reports identified 75 patients (27%) with pelvic nodal metastasis.

By contrast, 68Ga-PSMA-11 PET results were positive in 40 (14%), 2 (1%), and 7 (3%) patients for pelvic nodal, extrapelvic nodal, and bone metastatic disease, respectively.

The sensitivity of PSMA PET for pelvic nodal metastases was 0.40; specificity, 0.95; positive predictive value, 0.75; and negative predictive value, 0.81.

A total of 487 (64%) patients did not undergo prostatectomy, of which 108 were lost to follow-up. Patients with follow-up instead underwent radiation therapy (69%); systemic therapy (22%); surveillance (4%); or other treatments (5%).

The authors note, “It is clear that if the 68Ga-PSMA-11 PET is positive, then disease is present. On the other hand, the NPV was 0.81, indicating that 20% of patients who underwent prostatectomy with a negative PET will have nodes on pathology. For this reason, it is important that surgeons do not use a negative PET to forgo a pelvic nodal dissection.”

Dr. Hope added, “PSMA PET is only approved in a handful of countries and the US was one of the first to have a full approval of a PSMA PET radiotracer. The imaging studies are used under compassionate use in many other countries around the world.”

“Overall, this has historically led to significant disparities in access to the imaging study, as only those who could afford to travel were able to obtain (it),” he said. “The approval of both 68Ga-PSMA-11 and 18F-DCFPyL will help improve access and improve these disparities. Also, the recent inclusion of both PSMA PET radiotracers in the newly updated NCCN guidelines will help convince private insurers to cover the studies.”

Dr. Joseph Osborne of Weill Cornell Medicine in New York City, coauthor of a related editorial, commented in an email to Reuters Health, “This manuscript provided the context for FDA approval of one of the PSMA PET agents and a roadmap to guide the appropriateness of radical prostatectomy.”

“With the approval of 18F PSMA PET,” he noted, “we have two powerful new PSMA PET imaging tools to bring to the table for men in the fight against prostate cancer.”

Dr. Osborne said that he and his collaborators are “deeply committed” to broadening and access to these modalities “to address the well-known disparities with African American men.” He added, “This approval was an important first step.”

SOURCE: and JAMA Oncology, online September 16, 2021.

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