Imaging tool shows accuracy for lymph node staging

Munich-Positron emission tomography with a ⁶⁸Gallium-labeled ligand of prostate-specific membrane antigen (⁶⁸Ga-HBED-PSMA-PET hybrid imaging) is a promising new diagnostic tool for staging prostate cancer, according to German urologists who presented their experience at the American Society of Clinical Oncology annual meeting in Chicago.   

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They reported findings from a retrospective review including 332 consecutive patients with biochemical recurrence of prostate cancer after radical prostatectomy (median PSA, 1.7 ng/mL) who underwent the imaging technique to detect recurrent disease and from a study evaluating the accuracy of the technique for lymph node staging in 88 patients with primary intermediate- or high-risk prostate cancer. Collectively, the results indicate that ⁶⁸Ga-HBED-PSMA-PET hybrid imaging offers greater overall sensitivity and specificity than other current imaging techniques.

“We believe ⁶⁸Ga-HBED-PSMA-PET hybrid imaging has the potential to become a new standard in the evaluation of patients with prostate cancer for detecting sites of recurrence, identifying metastatic disease as part of the primary staging, and also as a guide for prostate biopsy,” said Jürgen Gschwend, MD, professor and chairman of urology at Technische Universität München in Munich, who was a co-author of both studies.

“We are now using it almost routinely in all men with prostate cancer biochemical recurrence and in the staging of men with primary clinically intermediate- or high-risk disease.”

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In the study of men with biochemical recurrence, the imaging was performed using computed tomography (CT) in 256 patients and with magnetic resonance (MR) in 76 patients. Analysis of outcomes with men stratified by PSA value showed ⁶⁸Ga-HBED-PSMA-PET hybrid imaging prostate cancer detection rates increased with increasing PSA values as follows: 96% (143/149) for men with PSA ≥2.0 ng/mL, 92% (80/87) for men with a PSA of 1.0 to 2.0 ng/mL, 72.3% (34/47) for men with PSA 0.5 to 1.0 ng/mL, and 53% (26/49) for men with a PSA 0.2 to 0.5 ng/mL. The results were similar in subgroup analyses dividing men according to whether they had imaging with CT or MR.

⁶⁸Ga-HBED-PSMA-PET hybrid imaging detected suspicious lesions missed by morphologic imaging techniques (CT or MRI scan alone) in almost one-third of the cohort, whereas it failed to identify lesions detected by other techniques in only nine men (2.7%). The detection rate was almost independent of PSA velocity, and it was not related to PSA doubling time.

NEXT: Detection rate high even in men with low PSA

Detection rate high even in men with low PSA

“It appears that the PSA value itself is what is important for determining the likelihood of a positive finding with ⁶⁸Ga-HBED-PSMA-PET hybrid imaging. However, the detection rate is high even in men with a relatively low PSA value and much better in those individuals than has been reported for other PET-tracers like 18F-FDG or choline derivatives,” Dr. Gschwend told Urology Times.

“We know from our study evaluating ⁶⁸Ga-HBED-PSMA-PET hybrid imaging for staging primary cancer that its specificity is very high, meaning that you can be pretty certain a positive signal is prostate cancer. Accurate identification of the site of metastasis with ⁶⁸Ga-HBED-PSMA-PET hybrid imaging in men with recurrent prostate cancer is critical information for informing management.”

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The study of ⁶⁸Ga-HBED-PSMA-PET hybrid imaging for staging primary cancer included 88 patients with intermediate- to high-risk disease who underwent the imaging prior to radical prostatectomy with pelvic lymph node dissection performed using a predefined template. Four other patients were excluded from the analysis because their primary cancer did not express PSMA.

Twenty patients were found to have positive lymph nodes on histologic evaluation, of whom 15 (75%) were identified with preoperative ⁶⁸Ga-HBED-PSMA-PET hybrid imaging. Histologic evaluation in the other five patients showed they only had micrometastasis in a single lymph node.

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In total, 470 lymph nodes were examined histologically, of which 52 were found to be positive. In the overall analysis of the 470 specimens, ⁶⁸Ga-HBED-PSMA-PET hybrid imaging demonstrated 73.1% sensitivity and 98.6% specificity with accuracy, positive predictive value and negative predictive value rates of 95.7%, 86.4%, and 96.7%, respectively.

Dr. Gschwend and colleagues have also recently reported on PSMA-radioguided surgery to identify metastatic lymph nodes intraoperatively in patients with primary or recurrent prostate cancer found to have nodal involvement by ⁶⁸Ga-HBED-PSMA-PET hybrid imaging (Eur Urol 2015; 68:530-4). The technique uses¹¹¹Indium-labeled PSMA ligand as the radiotracer.