Phase II, multi-center, interventional, non-randomized study

One dose ipilimumab on day 1 and after 1 week will receive SBRT (3x8Gy) on at least one but no more than 4 tumor lesions. Within one week of the last radiation fraction and after re-evaluation, patients will start with cemiplimab

Must still have measurable disease based on RECIST 1.1 after application of study SBRT. Lesions that were irradiated prior to the study, but have progressed since irradiation but prior to study inclusion will be allowed as measurable disease.

Must provide newly obtained tissue from a core or excisional biopsy of a tumor lesion and are willing to have a second biopsy performed from any non-irradiated lesion after the radiation and immune-modulating treatment. This lesion may be used for RECIST measurements.

Has a non-smoking-related targetable driver mutation, e.g. EGFR, ALK, RET or ROS1. Patients with advanced NSCLC with a smoking-related targetable driver mutation, e.g. KRAS or BRAF, may be found eligible if they have a history of ≥10 PY, but only when all options for targeted therapy have been exhausted and when progression on previous PD-(L)1 blockade has occurred.

Has had previous radical radiation to any tumor site within 3 months prior to study Day 1. Previous palliative radiation to any tumor site is not considered an exclusion criterion; however, this site will not be eligible for SBRT, biopsy location or RECIST tumor evaluation within this study