ESTRO 2022 - Abstract Book

S1072

Abstract book

ESTRO 2022

studies have shown a significant up-regulation of PD-L1 and CD8+ expression on tumor cells after chemotherapy, both radiotherapy and chemotherapy being able to induce an increase in PD-L1 expression due to their ability to induce DNA damage. The main purpose of this multicenter retrospective study is to evaluate the variation in PD-L1 expression before and after chemo-radiation treatment in patients with unresecable stage III NSCLC. Secondary objective are: Impact of the re-determination of PD-L1 expression on the therapeutic process approach (possibility of administering maintenance Durvalumab), acute complications of the rebiopsy. Materials and Methods Thirty-one patients with unresecable stage III NSCLC, PDL1 negative at onset, who underwent CRT and subsequently re- biopsied to re-determinate PDL1 status were enrolled by 20 Italian center. Pre- and post CRT histological samples were centralized in a single laboratory for the review of PD-L1 expression. The percentage of patients undergoing Durvalumab after CRT, the percentage of non-diagnostic procedures, the acute complications of re-biopsy were investigated Results The results of this study are still preliminary and complete analysis was archived in 7 patients. Median age was 68.2 months. All patients received radiotherapy treatment for a total dose of 60 Gy concomitant with cisplatin-based chemotherapy. The average time between the end of the CRT treatment and the start of Durvalumab was 54.6 months. Of all the patients analyzed, 2 currently showed a PDL1 expression switch with weak positivization (1% and 2% respectively) and this gave the opportunity to start Durvalumab maintenance treatment, while in the other cases the negative result was confirmed at the re-biopsy. Of the 2 patients with PDL1 positivization one developed disease progression and second-line chemotherapy was administered, while the second had a partial response and is continuing maintenance treatment. The re-biopsy procedure was well tolerated, however one patient experienced severe hypoxia requiring hospitalization, with recovery after two weeks Conclusion Although the data analysis is still ongoing, the present study is the first work in the literature evaluating the re- determination of PDL1 after CRT. The positivization of PDL1 after CRT is not a frequent event and could be burdened with severe rare side effects, however it guarantees an important therapeutic chance that can influence the overall survival of these patients. So, despite the results it is appropriate to discuss and identify in multidisciplinary board the patients who may be susceptible to re-biopsy 1 Gustave Roussy, Radiation Oncology, Villejuif, France; 2 Gudtave Roussy, Radiation Oncology, Villejuif, France; 3 Institut Claudius Regaud/Institut Universitaire du Cancer de Toulouse , Radiation Oncology, Toulouse, France; 4 Institut Claudius Regaud/Institut Universitaire du Cancer de Toulouse, Radiation Oncology , Toulouse, France; 5 Institut Claudius Regaud/Institut Universitaire du Cancer de Toulouse, Radiation Oncology , Radiation Oncology , Toulouse, France Purpose or Objective The role of local ablative treatments, including stereotactic body radiotherapy (SBRT), is an area of active research in oligometastatic non-small cell lung cancer patients. Small cell lung cancer (SCLC) has a poor prognosis, with common diffuse metastatic evolution. We evaluated the outcomes after SBRT in rare cases of oligoprogressive / oligorecurrent SCLC patients. Materials and Methods The data of SCLC patients who received SBRT for oligoprogressive / oligorecurrent disease in two French centers were retrospectively analyzed. Synchronous oligometastatic disease, SBRT for primary lung tumor and brain radiosurgery patients were not included in this analysis. Relapse and survival rates were defined as the time between the date of SBRT and the first event. Results Thirteen patients (male, 69%; n=7/13, all with initially limited stage), presenting 17 lesions were identified. All patients received prior treatments (thoracic chemoradiotherapy [n=7/13] and/or chemotherapy [n=6/13; median number of one line, range, 0-2 lines; only one received immunotherapy]) and the median ECOG PS was 1 (n=11/13). The main type of presentation was metachronous oligometastatic disease (n=10; vs 3 oligoprogression) and occurred at a median of 17.2 months after initial diagnosis. SBRT was delivered to one (n=9) to two (n=4) lesions (median size, 22 mm [range, 7-44 mm]) at a median dose of 48 Gy (range, 30-55 Gy) in 5 fractions (range, 5-10 fractions), mainly to lung [n=13/17] metastases. At a median follow-up of 3.2 years, no local relapse was observed but most (n=10) experienced distant relapse (DR). The median DR and overall survival rates were 3.6 months [95%CI: 2.5-13.7 months] and 12.6 months [95%CI: 7.5-29.9 months], respectively. The was no severe observed SBRT-related toxicities. Conclusion Prognosis was poor, with DR occurring in most patients. However, local control was excellent and long term response after SBRT may occur in oligoprogressive / oligorecurrent SCLC. Local ablative treatments should be discussed in a multidisciplinary setting on well-selected cases. PO-1272 SBRT for oligoprogressive/oligorecurrent SCLC: is it worth it? A. Levy 1 , A. Botticella 2 , E. Cohen-Jonathan Moyal 3 , C. Massabeau 4 , C. Le Péchoux 2 , J. Khalifa 5

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