A group of international experts representing the European Organisation for Research and Treatment of Cancer (EORTC) and European Society for Radiotherapy and Oncology (ESTRO) published in January 2020 issue of The Lancet Oncology consensus recommendations on oligometastatic disease classification and nomenclature. Furthermore, they plan to prospectively evaluate it within the OligoCare study.
The authors wrote in the background that Hellman and Weichselbaum in 1995 proposed oligometastatic disease as a distinct state between locally confined cancer and systemic metastatic disease.
The scarcity of biomarkers has made imaging the most relevant diagnostic method for defining oligometastatic disease. In particular, EORTC has identified the crucial role of imaging to standardise and optimise the clinical diagnosis of oligometastatic disease. These recommendations are intended to assist in the design of clinical trials.
Clinical trials design and clinical practice are currently consistent in limiting oligometastatic disease to a maximum of three to five metastases.
There is a luck of randomised phase III trials, but early clinical studies show improved survival when radical local therapy is added to systemic therapy for oligometastatic disease.
Despite the improvements in imaging and consensus on imaging-based definition of oligometastatic disease, clinical outcome after treatment of oligometastatic disease varies substantially. Several studies have proposed prognostic scoring systems or nomograms to achieve more accurate survival prediction and patient selection. However, all these studies are based on retrospective cohorts with potential bias in patient selection and none have been prospectively validated.
The limitations of clinical interpretation of imaging could substantially affect clinical outcomes. Therefore, better characterisation and classification of the different states of oligometastatic disease is needed.
Consensus recommendations on characterisation and classification of oligometastatic disease
A group of international experts in diagnosis and treatment of oligometastatic disease from the EORTC and ESTRO’s OligoCare project, initiated consensus process on characterisation and classification of oligometastatic disease with aim to establish a comprehensive system of oligometastatic disease characterisation factors, which should be assessed in all patients treated with radical local treatment for oligometastatic disease, both within and outside of clinical trials.
The oligometastatic disease characterisation factors were the basis to develop and agree on an oligometastatic disease classification system and nomenclature that cover all possible clinical situations of imaging findings with few metastases.
The authors wrote that the classification system should be unambiguous, based on established prognostic patient and disease characteristics, and not require additional diagnostic testing. They underlined that the classification system should also reflect fundamental biological and clinical processes underlying the development of oligometastatic disease and should be independent from the primary tumour type.
This project originates from the ESTRO and EORTC OligoCare registry project. The authors first performed a systematic review of the literature to identify inclusion and exclusion criteria of prospective interventional oligometastatic disease clinical trials. They used next a Delphi consensus process to select a total of 17 oligometastatic disease characterisation factors that should be assessed in all patients treated with radical local therapy for oligometastatic disease, both within and outside of clinical trials. By using a second round of the Delphi method, they established a decision tree for oligometastatic disease classification together with a nomenclature.
The authors agreed on oligometastatic disease as the overall umbrella term. A history of polymetastatic state before diagnosis of oligometastatic disease was used as the criterion to differentiate between induced oligometastatic disease considered as previous history of polymetastatic disease and genuine oligometastatic disease considered as no history of polymetastatic disease.
They further subclassified genuine oligometastatic disease into repeat oligometastatic disease considered as previous history of oligometastatic disease and de-novo oligometastatic disease considered as first-time diagnosis of oligometastatic disease. In de-novo oligometastatic disease, the authors differentiated between synchronous and metachronous oligometastatic disease.
They performed a final subclassification into oligorecurrence, oligoprogression, and oligopersistence, considering whether oligometastatic disease is diagnosed during a treatment-free interval or during active systemic therapy and whether or not an oligometastatic lesion is progressing on current imaging.
The authors plan to test these states of oligometastatic disease in the OligoCare prospective cohort trial (NCT03818503) to assess the prognostic value and the acceptance and compliance in routine practice. The primary objective of NCT03818503, E²-RADIatE (EORTC-ESTRO RADiotherapy InfrAstrucTure for Europe) is the collection of real-world data of cancer patients treated with radiotherapy.
Guckenberger M, Lievens Y, Bouma AB, et al. Characterisation and classification of oligometastatic disease: a European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer consensus recommendation. The Lancet Oncology 2020; 21(1): Pe18-e28.