CS01.03 Technical Reasons of Local Treatment Define the Limits of NSCLC OMD in Terms of Number of Metastases, Not a Fixed Number

Abstract

Currently there is no consensus on the definition of oligometastatic disease in NSCLC, with 3 or 5 lesions historically considered as the upper limit [1]. A low number of metastases, indeed, is a good although not perfect surrogate of the biology behind the oligometastatic state. In real life practice, the number of metastatic lesions is often misleading, since it is possible to find patients with more than 5 metastases affected by a slowly progressing disease, potentially taking advantage from local treatments. On the contrary, patients affected by just one or two metastases can progress very rapidly with a dismal prognosis, despite the apparent low disease burden. Since the number of metastases is not a perfect indicator of oligometastatic state and biomarkers really able to identify this disease are lacking, there is a trend favoring the technical feasibility of local treatment over the number of metastases to treat. This approach has pros and cons. On one side, the idea of killing all visible cancer cells independently by their number is appealing and possibly with a positive impact on patient prognosis. On the other side, clinical data supporting such an aggressive local treatment have still a low level of evidence. Moreover, the definition of “technically feasible” is quite vague, particularly in the world of radiation oncology. Indeed, radiotherapy is strongly related to technological development. The innovations in this setting have dramatically increased the possible indications of radiotherapy, also for oligometastases. With state of the art radiotherapy, we are now able to treat virtually all sites in the body and it is becoming really difficult to define an upper limit to the number of lesions that can be treated. However, this is feasible only with advanced technologies, like image guided radiotherapy (IGRT), motion management (4D CT, gating, tracking, etc.), and heavy particles in particular clinical settings (retreatment for instance). This trend is creating a gap between Radiation Therapy Departments, since some treatments are becoming safely deliverable only in well selected Institutions with high expertise in this field. Despite all recent technological achievements, some clinical settings remain in which the risk-benefit ratio should be carefully weighted before delivering ablative dose to a metastatic patient. For instance, there are still uncertainties in the treatment of central lung lesions abutting on the main bronchus [2] or, changing scenario, the amount of remaining healthy liver is still limiting liver metastases treatment in some situations [3]. More importantly, the goal of local treatment of an oligometastatic patient should be to change the natural history of the tumor, independently from the number of metastases we are able to treat. Treating all the metastases, even though safely feasible, remains just a technical exercise if no impact on prognosis, quality of life or symptoms control is achievable. Oligometastatic disease has definitely a different biology, and every effort should be in the direction of identifying this biology [4]. Technologies have developed faster than our clinical and biological knowledge, and this should be kept in mind. In conclusion, the number of metastases remains a good clinical indication of oligometastatic state, but this number should not be an insuperable limit in clinical practice. Technical feasibility of local treatments (as radiotherapy) should be always carefully weighted accounting for risk-benefit ratio. Being able to treat any number of metastases should not be considered as a good reason for doing it indiscriminately. Physicians should always consider the clinical and biological reasons for a local ablative treatment in a metastatic patient, independently by technical issues. [1] Hong JC, Salama JK. The expanding role of stereotactic body radiation therapy in oligometastatic solid tumors: What do we know and where are we going? Cancer Treatment Reviews 52 (2017) 22–32 [2] Videtic GM, Donington J, Giuliani M et al. Stereotactic body radiation therapy for early stage non-small cell lung cancer: Executive Summary of an ASTRO Evidence-Based Guideline. Practical Radiation Oncology (2017) 7, 295-301 [3] Mondlane G, Ureba A, Gubanski M et al. Estimation of the risk for radiation-induced liver disease following photon- or proton-beam radiosurgery of liver metastases. Radiat Oncol. 2018 Oct 22;13(1):206. https://doi.org/10.1186/s13014-018-1151-6 [4] Correa RJ, Salama JK, Milano MT et al. Stereotactic Body Radiotherapy for Oligometastasis Opportunities for Biology to Guide Clinical Management. Cancer J. 2016 Jul-Aug;22(4):247-56. Oligometastases, SBRT, NSCLC