ESTRO 2023 - Abstract Book

S425

Sunday 14 May 2023

ESTRO 2023

evaluations. So, even though we don’t need PTV margins in proton therapy, robust planning methods that replaced PTV planning include setup errors with magnitudes in agreement with PTV margins. Voxel-wise minimum dose evaluations are highly correlated to PTV dose evaluations, including corresponding plan acceptance criteria. Despite major changes introduced with robust planning, links to PTV planning remain.

SP-0526 Do we need PTV margins in brachytherapy? K. Tanderup Denmark

Abstract not available

Joint Symposium: ESTRO-IASLC: New treatment strategies for stage III NSCLC and innovative biomarkers for patient's selection and monitoring

SP-0527 New neoadjuvant/adjuvant strategies for resectable disease L. Hendriks 1 1 Maastricht UMC, Pulmonary Diseases, Maastricht, The Netherlands

Abstract Text In resectable non-small cell lung cancer (NSCLC), both neoadjuvant as well as adjuvant chemotherapy result in an 5% gain in overall survival (OS) at 5 years. However, especially for stage II and III NSCLC, 5 year OS is still poor, and the majority of patients with a disease relapse have a distant relapse. Therefore, systemic therapies (neoadjuvant and/or adjuvant) should be improved. Adjuvant MAGE-A3, gefitinib as well as bevacizumab did not improve outcomes. Neoadjuvant therapy has the advantage that patients are still fit, and that the efficacy of the neoadjuvant therapy can be evaluated in the resection specimen. Disadvantage is that some patients will not proceed to surgery, either due to disease progression or due to complications of the systemic therapy. Adjuvant therapy has the advantage that the patient underwent the curative intent resection, but the disadvantage is the higher risk of not receiving adjuvant therapy due to postoperative complications resulting in a delayed recovery. Preferably, new systemic therapies eradicate microscopic disease, without increasing the rate of complications or long-term toxicities. Furthermore, early endpoints associated with OS are preferred to early implement new strategies. In locally advanced as well as metastatic NSCLC, immunotherapy has become standard of care. Furthermore, for patients with an activating EGFR mutation, tyrosine kinase inhibitors (TKI) have become standard of care in the metastatic setting, as well as in the adjuvant setting. In this presentation I will give an overview of the completed phase III immunotherapy trials (CheckMate816, IMpower010, PEARLS) and ongoing trials, and I will discuss open questions regarding neoadjuvant and adjuvant immunotherapy. Furthermore, I will discuss the completed phase III EGFR-TKI trials including their differences and the implications and open questions. SP-0529 The challenge of equipoise when comparing surgical vs. non-surgical strategies in stage III NSCLC J. Remon 1 1 gustave Roussy, Medicine, Villejuif-Paris, France Abstract Text After the introduction of immune checkpoint blockers (ICB), either anti-PD1 or anti-PD-L1, this strategy has been included in the therapeutic strategy of patients with an early-stage non-small cell lung cancer (NSCLC). Stage III NSCLC remains an heterogenous disease and based on the new date with ICB we can apply this strategy either in the neoadjuvant strategy in combination with chemotherapy (CheckMate 816 trial, NADIM-2 trial) or in the adjuvant setting (IMpower 010 trial with adjuvant atezolizumab, mainly restricted to tumors with high PD-L1 expression, those with PD-L1 ≥ 50%, and the PEARLS trial with adjuvant pembrolizumab not yet approved by health authorities). For unresectable stage III NSCLC, consolidation treatment for 1 year after radical chemo-radiotherapy is the standard of care in PD-L1 ≥ 1% positive tumors by the EMA or in all comers by the FDA. However, even today, it is still challenging the definition of resectability criteria in stage III NSCLC worldwide, being even more relevant after the introduction of ICB in the therapeutic strategy positively impacting in the outcome. Also, among stage III tumors considered resectable upfront there is no face-to-face trial comparing between neoadjuvant concurrent chemo-immunotherapy versus adjuvant chemotherapy followed by sequential immunotherapy for 1 year. Indeed, in the adjuvant ICB trials, probably most of patients with stage III enrolled are patients with unforeseen N2 disease that may have a different oncologic prognostic compared with those NSCLC with upfront IIIAN2. In this situation, potential treatment duration (9 weeks -3 cycles- with neoadjuvant strategy vs 1 year with adjuvant immunotherapy), percentage of R0 resection after neoadjuvant strategy, treatment compliance, and potential risk of late toxicities in prolonged treatment exposure could be factors to take into account for deciding the best approach if we want to introduce ICB in the strategy of resectable stage III NSCLC. For instance, there are no robust predictive biomarkers, and PD-L1 positive tumors obtain better benefit regardless of the strategy adjuvant or neoadjuvant. In the unresectable stage III disease, the PACIFIC trial reported that consolidation treatment with durvalumab after radical chemo-radiotherapy significantly improved the progression free survival and the overall survival compared with placebo. In the trial 48% of patients had stage IIIAN2, so not clear that these patients could be considered unresectable for all the thoracic surgeons. This may introduce a new challenge, should patients with resectable stage III NSCLC receive surgery in the immunotherapy era? What is the best local treatment strategy in this setting? Finally, we need to redefine the TNM and probably TNM is not the unique tool that we should use in the coming future for defining stage III. In this sense, circulating tumor DNA (ctDNA) may help to define tumors with poorer prognostic in case that ctDNA is positive at baseline. Finally in the recent years we are living SP-0528 New strategies for unresectable disease S. Ramella Italy Abstract not available