Study: PSMA PET/CT Agent May Rule Out csPCa in 93 Percent of PI-RADS 3 Lesions

For the detection of clinically significant prostate cancer (csPCa), emerging research showed the use of 18F-PSMA-1007 positron emission tomography/computed tomography (PET/CT) accurately differentiated 65 percent of PI-RADS 3 lesions.

That is one of the findings from a new prospective study, recently published in Radiology, which examined the use of 18F-PSMA-1007 PET/CT in 75 men (median age of 67) with elevated prostate-specific antigen (PSA) levels (median 7 ng/mL) who previously had multiparametric magnetic resonance imaging (mpMRI) exams. Out of 102 detected lesions, 68 were PI-RADS 3 or higher lesions, according to the study.

On a per-participant basis, the researchers found that 18F-PSMA-1007 PET/CT provided a 91 percent sensitivity rate in comparison to 95 percent for mpMRI in detecting csPCa. The study authors also noted that 18F-PSMA-1007 PET/CT had a 62 percent specificity rate in contrast to 45 percent for mpMRI.

Study: PSMA PET/CT Agent May Rule Out csPCa in 93 Percent of PI-RADS 3 Lesions

Here one can see pre-biopsy imaging, including mpMRI and 18F-PSMA-1007 PET/CT scans, revealing clinically significant prostate cancer (csPCa) with a PI-RADS 3 lesion. A recent prospective study found that 18F-PSMA-1007 PET/CT had a 91 percent sensitivity rate for diagnosing csPCa and a 93 percent negative predictive value (NPV) for ruling out csPCa in PI-RADS 3 lesions. (Images courtesy of Radiology.)

For PI-RADS 3 lesions, the researchers noted a 93 percent negative predictive value (NPV) for 18F-PSMA-1007 PET/CT as use of the agent led to upgrading or downgrading of these lesions in 17 of 26 study participants (65 percent).

“ … For PI-RADS 3 lesions, where radiologists are uncertain about the presence of PCa, 18F-PSMA-1007 PET/CT seemed useful, as PET was able to help correctly distinguish between tumor tissue and benign disease in 65% of lesions due to a particularly high NPV of more than 90%,” wrote lead study author Bastiaan M. Prive, M.D., Ph.D., who is affiliated with the Department of Medical Imaging and Nuclear Medicine with the Radboud University Medical Center at the Radboud Institute for Health Sciences in Nijmegen, the Netherlands, and colleagues.

The researchers also noted key attributes with 18F-PSMA-1007 PET/CT that may make it a viable alternative to other PET/CT imaging agents.

“In this setting, fluorine 18 (18F) PSMA-1007, a novel radiolabeled PSMA ligand, is particularly attractive due to its low renal excretion, improving the visibility of PSMA-positive foci in proximity to the urinary tract (i.e., the prostate) compared with other PSMA tracers. Moreover, the lower positron energy of 18F offers higher resolution than gallium 68 (68Ga)–labeled compounds (e.g., Ga-PSMA-11),” added Prive and colleagues.

In an accompanying editorial, Baris Turkbey, M.D., emphasized the adjunctive possibilities of 18F-PSMA-1007 PET/CT in mitigating the challenges of indeterminate PI-RADS 3 lesions.

“The study by Prive et al confirms the potential of 18F-PSMA-1007 PET/CT as a tool that is complementary to mpMRI in the diagnosis of PCa. While demonstrating good sensitivity and moderate specificity, this hybrid approach notably excels in ruling out clinically significant PCa in PI-RADS 3 lesions,” said Dr. Turkbey, a senior clinician with the Molecular Imaging Branch of the National Cancer Institute at the National Institutes of Health (NIH).

(Editor’s note: For related content, see “PET/CT or mpMRI: Which is Better for Detecting Biochemical Recurrence of Prostate Cancer?,” “Study: PET/MRI May Prevent Up to 83 Percent of Unnecessary Biopsies in Men with PI-RADS 3 Lesions” and “New Research Evaluates PI_RADS Upgrading Rules in MRI Exams for Prostate Cancer.”)

In regard to study limitations, the authors noted inconsecutive patient enrollment, an underpowered sample size and possible confirmation bias due to awareness of mpMRI findings by the nuclear medicine physicians. The researchers also conceded that performance of the study at a MRI referral facility may limit extrapolation of the study findings to a broader population.

Three Key Takeaways

  1. High NPV for PI-RADS 3 lesions. The study highlights the significant utility of 18F-PSMA-1007 PET/CT in distinguishing between tumor tissue and benign disease in PI-RADS 3 lesions, with a high negative predictive value (NPV) of 93 percent. This means that the use of this imaging method can effectively rule out clinically significant prostate cancer (csPCa) in cases where radiologists are uncertain.

  2. Comparative diagnostic performance: The research shows that 18F-PSMA-1007 PET/CT has a sensitivity rate of 91 percent and a specificity rate of 62 percent for detecting csPCa, compared to 95 percent sensitivity and 45 percent specificity for mpMRI. This indicates that while mpMRI has a slightly higher sensitivity, 18F-PSMA-1007 PET/CT offers improved specificity, making it a valuable complementary tool in prostate cancer diagnosis.

  3. Advantages of 18F-PSMA-1007: The study points out that 18F-PSMA-1007 has beneficial properties such as low renal excretion and higher resolution due to lower positron energy, making it more effective for visualizing PSMA-positive foci near the urinary tract. These attributes suggest that 18F-PSMA-1007 PET/CT could offer improved visualization compared to other PET tracers like gallium 68-labeled compounds.