Defining Synchronous Oligometastatic Non–Small Cell Lung Cancer: A Systematic Review

Introduction: Synchronous oligometastatic (sOM) disease is an oncological concept characterized by a limited cancer burden. Patients with oligometastasis could potentially benefit from local radical treatments. Despite the fact that the sOM condition is well recognized, a universal definition, including a specific definition for NSCLC, is not yet available. The aim of this systematic review was to summarize the definitions of and staging requirements for use of the term synchronous oligometastatic in the context of NSCLC. Methods: The key issue was formulated in one research question according to the population, intervention, comparator, and outcomes strategy. The question was introduced in MEDLINE (OvidSP). All articles dealing with sOM NSCLC and providing a definition of synchronous oligometastasis in NSCLC were selected and analyzed. Results: A total of 21 eligible articles focusing on sOM NSCLC were retrieved and analyzed. In 17 studies (81%), patients had to be staged with magnetic resonance imaging or computed tomography of the brain, thoracic and abdominal computed tomography, and positron emission tomography. The total number of metastases allowed in the definitions ranged from one to eight, but in 38.1% of studies the maximum number was 5. Most of the publications did not define the number of involved organs or the maximum number of metastases per organ. For mediastinal lymph node involvement, only five articles (27.8%) counted this as a metastatic site. Conclusions: No uniform definition of sOM NSCLC could be retrieved by this systematic review. However, extended staging was mandated in most of the studies. An accepted oncological definition of synchronous oligometastasis is essential for patient selection to define prospective clinical trials.