In the current landscape, there is no standardized definition of oligometastatic disease. At a recent meeting in St. Gallen, Switzerland, the Advanced Prostate Cancer Consensus Conference, world experts were asked “What is the most meaningful definition of oligometastatic prostate cancer?” The majority (84.8%) agreed that the definition should be ≤3 synchronous metastases (bone and/or lymph nodes), although a proportion of delegates (12.1%) felt this number should be ≤5 synchronous metastases.
How we diagnose these patients is also challenging, as Dr. Tombal notes that the imaging landscape is rapidly evolving. Traditionally we have used Tc99m bone scintigraphy, however there has been emergence of whole body MRI to enhance ability to diagnose soft tissue lesions. Furthermore, we have seen an abundance of studies (nearly 250 studies published in 2016, compared to ~50 studies in 2015) assessing the role of PSMA PET in advanced prostate cancer, which carries high diagnostic value but demonstration of clinical benefit is still pending.
For high/very high risk prostate cancer patients (up to T4/N1) standard of care may be local treatment + lymph node template based treatment, however new imaging technologies are allowing patients to be assessed for whether they are truly localized or have oligometastatic disease. According to Dr. Tombal, the question is “not about local treatment but about adding local treatment of metastasis deposits outside the lymph node base template.” A study from 2015 assessed 15 single-arm case series reporting on 450 patients with metastasis directed therapy of regional and distant recurrences after curative treatment showed that some men will derive a progression-free survival benefit (51% progression free 1-3 years after salvage therapy) , although these studies are clearly prone to selection biases.
Given Level 1 evidence in the EAU-ESTRO-ESUR-SIOG guidelines, Dr. Tombal highlighted that all patients with M1 disease at diagnosis should be offered castration therapy in combination with docetaxel. A recent meta-analysis of the randomized controlled trials demonstrated that the addition of docetaxel was associated with a significant survival advantage (HR 0.77; 95%CI 0.68-0.87)  in this patient cohort.
In summary, Dr. Tombal warned about new imaging technologies and how we discuss/treat metastatic patients, noting “Don’t trust everything you see. Even salt looks like sugar.” A final word of caution provided by Dr. Tombal is provided by the definition of the ‘band-wagon effect’: “A phenomenon whereby the rate of uptake of beliefs, ideas, fads and trends increases the more that they have already been adopted by others.” To answer the potential therapeutic benefit of treating oligometastatic disease, we require and anticipate data from ongoing clinical trials.
1. Ost P, Bossi A, Decaestecker K, et al. Metastasis-directed therapy of regional and distant recurrences after curative treatment of prostate cancer: A systematic review of the literature. Eur Urol 2015;67(5):852-863.
2. Vale CL, Burdett S, Rydzewska LH, et al. Addition of docetaxel or bisphosphonates to standard of care in men with localized or metastatic, hormone-sensitive prostate cancer: A Systematic review and meta-analyses of aggregate data. Lancet Oncol 2016;17(2):243-256.
Speaker(s): Bertrand Tombal, Cliniques universitaires Saint-Luc Universite catholique de Louvain, Brussels, Belgium
Written By: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto
at the #EAU17 - March 24-28, 2017- London, England