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Researchers develop the first definitive classification system for oligometastatic disease

Oligometastatic disease (OMD) is an intermediate state where a primary cancer has spread (metastasised) to a limited number of regions. Recent studies suggest that patients in this state have a better chance of survival when eradication of all visible disease by radical local therapy is added to standard systemic therapy. However, the outcome of patients treated with such curative intent varies substantially, indicating that oligometastasis is not a homogeneous cancer state. But there is little consensus on how best to characterise and classify these different states of OMD.

Now, for the first time, a team of international experts from the European Organisation for Research and Treatment of Cancer (EORTC) and the European Society for Radiotherapy and Oncology (ESTRO) have developed a comprehensive system for the classification of OMD. “Studies seem to show that adding radical local therapy to systemic treatment for OMD can improve survival,” says Professor Dr Matthias Guckenberger, Chairman of the Department of Radiation Oncology, University Hospital of Zurich, Zurich, Switzerland, who led the research. “However, to date no biomarkers for OMD have been identified, so diagnosis is based predominantly on imaging findings. Our new classification system will not only improve the selection of treatment for individual patients but will also contribute to a better understanding and interpretation of study results.”

In a paper published in The Lancet Oncology on 2nd January 2019, the researchers describe how they carried out a literature review in order to decide which prospective interventionist clinical trials to include in their study. They identified and agreed on 17 OMD characteristics that needed to be assessed in all those patients who underwent radical local treatment, both in and outside of clinical trials. These initial steps allowed a more detailed subclassifications of OMD.

Although imaging is currently essential in the diagnosis of OMD, it is unable to distinguish between, for example, patients with tumours at an early stage of progression with a limited number of metastases, and those who had had widespread metastases and where a few remained after chemotherapy treatment. “These two scenarios can appear very similar on imaging, but are likely to be associated with very different outcomes, and will require different treatment strategies,” says Professor Dr Yolande Lievens from the Department of Radiation Oncology, Ghent University Hospital, Ghent, Belgium, one of the authors on the paper. “So we were pleased to be able to identify five binary disease classification factors that form a sound basis for OMD characterisation.”

“Although the use of this classification as a definitive decision-making tool still needs to be confirmed, we believe that these disease characteristics should be assessed in all cancer patients treated with radical local treatment for OMD. They should also allow harmonisation of reporting and therefore allow outcome analyses of improved quality,” says co-author Professor Dr Piet Ost from the Department of Radiation Oncology, Ghent University Hospital, Ghent, Belgium.
In the context of clinical trials, a harmonised characterisation system will contribute to a better understanding and interpretation of study results and facilitate cross-study comparisons, meta-analyses and systematic reviews. “Importantly, acceptance and implementation of OMD-related clinical trials into clinical practice will be facilitated by such a clear and unambiguous classification system and nomenclature,” says Prof Dr Guckenberger.

The researchers will follow up their work in the E2-RADIatE (EORTC-ESTRO Radiation Infrastructure for Europe) OligoCare trial, which will investigate further which treatment is best suited to individual patients with OMD. “In the past, without a robust classification system, this was very difficult,” says Prof Dr Guckenberger. “We are looking forward to further assessment of the prognostic value of our findings and hope to see their rapid adoption into clinical practice.”

1 Characterisation and classification of oligometastatic disease: a European Society for Radiotherapy and Oncology and European Organisation for Research and Treatment of Cancer consensus recommendation. M. Guckenberger, Y. Lievens, A. B. Bouma, L. Collette, A. Dekker, N. M. deSouza, A-M.C. Dingemans, B. Fournier, C. Hurkmans, F. E. Lecouvet, I. Meattini, A. Méndez Romero, U. Ricardi, N. S. Russell, D. H. Schanne, M. Scorsetti, B. Tombal, D. Verellen, C. Verfaillie, P.Ost; The Lancet Oncology. 2020;

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