Margriet Kwint

Outcome of treatment of synchronous oligometastases 51 3 Introduction Lung cancer is the leading cause of cancer death, with 1.59 million deaths annually worldwide [1]. More than half of the patients with non-small cell lung cancer (NSCLC) are diagnosed with metastatic disease [2]. According to current treatment guidelines, stage IV NSCLC patients are considered incurable and are mainly treated with palliative intent [3]. Nonetheless, the treatment options of stage IV NSCLC patients have increased with a tendency towards a more personalized treatment approach. When a patient has a limited number of metastases (also called ‘oligo metastasis’ [4,5]), a more radical treatment regime instead of palliative treatment may be beneficial with respect to progression free and/ or overall survival [6]. Hellman and Weichselbaum first described the term ‘oligometastasis’ in 1995 [4,5]. According to this concept, radical/aggressive local cancer treatments might be curative in a proportion of patients with a limited amount of metastases. However, the existing literature is seriously flawed by the lack of a general consensus on the definition of oligometastatic disease. A commonly used definition in the literature is ‘metastases limited in number and destination organ’. However, the specific number is not consistently formulated. Often a maximum of 2 metastases are referred to as oligometastatic disease, and treated accordingly [7,8]. In contrast, ≤5 metastases are also mentioned as oligometastatic disease and considered for radical treatment [7] . Considering the lack of a proper definition for oligometastatic disease, there is a need to investigate the association between the number of metastases and survival in stage IV NSCLC patients. Limited retrospective data are available in literature on oligometastatic NSCLC, both on synchronous and metachronous metastases and on heterogeneous treatments including surgery, stereotactic ablative radiotherapy and radical radiotherapy [7-27]. In a recent systematic review on the evidence for the oligometastatic theory in NSCLC, Ashworth et.al . [7] concluded that: “Long-term survivors do exist. Radical treatment of the primary lung tumor and metastases are strongly associated with improved long-term survival”. Gomez et.al [14] reported the outcome of a prematurely terminated phase II randomized trial. In this trial, patients with oligometastatic NSCLC without progression after first line systemic therapy were randomized between local consolidative therapy versus maintenance therapy or observation. The outcome showed improved progression free survival for those patients treated with local consolidative therapy.