EAU 2018: Novel Modalities for Nodal Staging in Prostate Cancer
Secondary to less neovasculature in nodal metastasis, these lesions are less sensitive to systematic therapy. So, according to Dr. van der Poel, the question remains: is there a survival benefit for lymphadenectomy for patients with prostate cancer? The answer is likely maybe, according to Dr. van der Poel, particularly when multimodal therapy is involved, such as radiotherapy and ADT treating “remnant” disease even after extended lymphadenectomy. Previous studies have suggested that the optimal number of lymph nodes to remove is 14, with the number of removed lymph nodes independently predicting lower cancer specific mortality (HR 0.93, p=0.02) [1]. A recent update of the Briganti nomogram suggests that an optimal cutoff of 7% (rather than 5%) when selecting patients for extended pelvic lymph node dissection [2]. At this cutoff, this would spare 70% of patients an extended pelvic lymph node dissection at the cost of missing only 1.5% positive lymph nodes.
In the last several years the utility of PET scan imaging has emerged, namely 18F-FDG PET (low sensitivity), 18F-fluoride PET (for bone metastasis), 18F/11C Choline PET (low sensitivity), and 18F/68Ga-PSMA PET (>80% sensitivity). In an analysis of 16 studies (n=1,309) assessing patients with advanced prostate cancer at PSA <0.02, 68Ga-PSMA PET had a positivity rate of 42% and an overall sensitivity/specificity per lesion of 80%/97% [3]. However, detecting lymph nodes on PSMA-PET imaging may not be enough, as a recent study found that 36% of PSMA-positive nodes were not included in the pelvic radiation template [4]. Other recent technologic advances for identifying lymph node positivity include: 99mTc-PSMA for intraoperative identification of positive lymph nodes, nanoMRI, multimodal tracing, sentinel lymph node + 68Ga-PSMA PET, the Firefly option for the da Vinci Si, and SentiMagPro, which is magnetic resonance for sentinel lymph node imaging.
As Dr. van der Poel notes, imaging microscopic metastases will remain illusive, while it may be these patients that benefit from detection and treatment. He summarized by stating that nodal imaging is certainly a new niche for detection and treatment of prostate cancer, novel imaging enhances detection rates, the sensitivity of small metastases (< 3mm) remains low, and there is still work to do regarding optimal template vs stereotactic treatment.
Presented by: Henk G. van der Poel, Leiden University Medical Center, Leiden, The Netherlands
Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre, twitter: @zklaassen_md at the 2018 European Association of Urology Meeting EAU18, 16-20 March, 2018 Copenhagen, Denmark
References:
1. Abdollah F, Gandaglia G, Suardi N, et al. More extensive pelvic lymph node dissection improves survival in patients with node-positive prostate cancer. Eur Urol 2015;67(2):212-219.
2. Gandaglia G, Fossati N, Zaffuto E, et al. Development and internal validation of a novel model to identify the candidates for extended pelvic lymph node dissection in prostate cancer. Eur Urol 2017;72(4):632-640.
3. Perera M, Papa N, Christidis D, et al. Sensitivity, specificity, and predictors of positive 68GA-prostate-specific membrane antigen positron emission tomography in advanced prostate cancer: A systematic review and meta-analysis. Eur Urol 2016;70(6):926-937.
4. Schiller K, Devecka M, Maurer T, et al. Impact of 68Ga-PSMA-PET imaging on target volume definition and guidelines in radiation oncology – a patterns of failure analysis in patients with primary diagnosis of prostate cancer. Radiat Oncol 2018;13(1):36.