TPS8585 Background: Non-small cell lung cancer (NSCLC) is the most common cause of cancer death worldwide highlighting the importance of improving current therapeutic options. In particular, elderly and frail patients are not only underrepresented in clinical trials, but also frequently do not receive standard treatment regimens due to comorbidities. For example, patients with unresectable stage III NSCLC who are unfit for chemotherapy (CHT) do not benefit from the recent seminal therapy algorithm change for this disease, i.e. consolidation therapy with the immune checkpoint inhibitor (ICI) durvalumab after combined radiochemotherapy (RChT). Instead, these patients are treated with radiotherapy only, raising the serious concern of undertreatment. This issue is addressed by the TRADE-hypo clinical trial that investigates a novel therapy option for NSCLC stage III patients not capable of receiving CHT. To this end, thoracic radiotherapy (TRT) is administered together with durvalumab, employing the synergism created by the combination of restoring anti-tumor immune response by the ICI with the induction of immunogenicity by irradiation. The latter effect has been suggested to be further boosted by hypofractionated radiotherapy, which could also be more practicable for the patient. Taken these considerations into account, the TRADE-hypo trial addresses safety and efficacy of durvalumab therapy combined with either conventional or hypofractionated TRT. Methods: The TRADE-hypo trial is a prospective, randomized, open-label, multicentric phase II trial. Eligible patients are diagnosed with unresectable stage III NSCLC and not capable of receiving sequential RChT due to high vulnerability as reflected by a poor performance status (ECOG 2 or ECOG1 and CCI≥ 1) and/or high age (≥ 70)]. Two treatment groups are evaluated: Both receive durvalumab (1,5000 mg, Q4W) for up to 12 months. In the CON-group this is combined with conventionally fractionated TRT (30 x 2 Gy), while in the HYPO-group patients are treated with hypofractionated TRT (20 x 2.75 Gy). In the HYPO-arm, a safety stop-and-go lead-in phase precedes full enrollment. Here, patients are closely monitored with regard to toxicity (i.e., pneumonitis grade ≥ 3 within 8 weeks after TRT) in small cohorts of 6. The primary objective of the trial is safety and tolerability. As a primary efficacy endpoint, the objective response rate after 3 months will be evaluated. Further endpoints are additional parameters of safety and efficacy, as well as the comprehensive collection of biomaterials to be analyzed regarding treatment-induced changes and potential novel biomarkers. As of February 10, 2021, 9 patients of planned 88 patients have been enrolled in the TRADE-hypo trial. Clinical trial information: NCT04351256.