Margriet Kwint

General discussion and future perspectives 153 8 Patient selection for oligometastatic disease Patients with stage IV NSCLC are considered incurable and are mainly treated with a palliative intent (25). However, when a patient presents with a limited number of metastases (oligometastatic disease), a more radical treatment regime instead of palliative treatment may be beneficial with respect to PFS and/or OS (26-29). Chapter 3 describes the results of a retrospective cohort study of stage IV NSCLC patients (N=91) with ≤5 synchronous oligometastatic disease with a good performance status, who were treated with a radical treatment at the NKI (either with surgery or radiotherapy after systemic treatment). Favorable long-term PFS and OS (14 and 32 months, respectively) was found in this selected group of patients, compared to stage IV NSCLC patients who were treated with palliative chemotherapy only (1-year OS of 29% and a median OS of 6 months) (25). Ideally, the benefits of a radical treatment for oligometastatic NSCLC are investigated within randomized phase III trials. Several randomized phase II trials showed improved treatment outcomes for an additional local consolidative treatment of the oligometastases compared to systemic treatment only as the standard of care (27-31). Two of these randomized studies were prematurely closed after interim analysis, due to a significant PFS benefit in the local consolidative therapy arm (27, 31). To learnmoreabout theoutcomeof a radical local treatment foroligometastaticdisease and the different states of oligometastatic disease, it is crucial that internationally, the same definitions are used. ESTRO and EORTC recently published a consensus report on the different states of oligometastatic disease (29). They distinguish 9 different states of oligometastatic disease as shown in Figure 1 (29). Consequently, the committee set up the OligoCare prospective multi-cohort trial with the aim to assess the prognostic value of the defined oligo states and the acceptance and compliance of these states within clinical practice (NCT03818503) (32). Besides uniform definitions of the different states of oligometastatic disease, another important knowledge gap is the number of metastases present to be considered for oligometastatic state. Currently, a maximum of 3-5 metastases is most often called oligometastatic disease (29, 33, 34). In our study, most patients had 1 metastasis (85%), with a maximum of 4 metastases. The SABR-COMET study (28) was a randomized phase II study in which 99 patients with a maximum of 5 synchronous metastases were randomized between either palliative standard of care or standard of care + SABR to all metastatic lesions. In this study, SABR was associated with improved OS compared to palliative care (me-