characterization of MPM heterogeneity by identifying new significant associations between mutational status and histologic and molecular heterogeneity. Strikingly, we highlight the strong association between new mutations and overall survival.

Nivolumab is now a reference treatment for patients with advanced non-small cell lung cancer (NSCLC) after failure of prior platinum-based chemotherapy. Little data are available on treatment approaches following discontinuation of nivolumab and on the interest of a second course of immunotherapy after nivolumab discontinuation. The aims of this study were to describe treatment pathways following nivolumab discontinuation and to describe survival following retreatment with immunotherapy. Materials and methods: The analysis includes all patients with NSCLC recorded in a national hospital database, starting nivolumab in 2015-2016. Nivolumab treatment was considered discontinued if ≥3 infusions were missed. Patients starting a second course of PD-1 inhibitor following nivolumab discontinuation were analysed according to the duration of their initial nivolumab treatment course. Results: 10,452 patients were included (71 % men; mean age: 63.8 ± 9.6 years; squamous histology: 44 %). Median nivolumab treatment duration was 2.8 months [IQR :1.4-6.9]. Median OS was 11.5 months [95 %CI: 11.1-11.9]; 5118 (53.4 %) patients received post nivolumab therapy lines: 1517 (29.6 %) of these received a second course of PD-1 inhibitor, either after a treatment-free interval (resumption: n = 1127) or after intervening chemotherapy (rechallenge: n = 390). Median OS after nivolumab discontinuation was 15.0 months [13.9-16.7] in the resumption group and 18.4 months [14.8-21.9] in the rechallenge group. Median OS was significantly longer in patients with an initial nivolumab treatment duration ≥3 months. Conclusion: In this real-world setting, outcome after retreatment with a PD-1 inhibitor following a first course of nivolumab was significantly better in patients with a longer duration of initial nivolumab treatment.

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Background Malignant pleural mesothelioma (MPM) is a heterogeneous cancer. Better knowledge of molecular and cellular intra-tumor heterogeneity throughout the thoracic cavity is required to develop efficient therapies. This study focuses on molecular intra-tumor heterogeneity using the largest series to date in MPM and is the first to report on the multi-omics profiling of a substantial series of multi-site tumor samples. Methods Intra-tumor heterogeneity was investigated in 16 patients from whom biopsies were taken at distinct anatomical sites. The paired biopsies collected from apex, side wall, costo-diaphragmatic, or highest metabolic sites as well as 5 derived cell lines were screened using targeted sequencing. Whole exome sequencing, RNA sequencing, and DNA methylation were performed on a subset of the cohort for deep characterization. Molecular classification, recently defined histo-molecular gradients, and cell populations of the tumor microenvironment were assessed. Results Sequencing analysis identified heterogeneous variants notably in NF2, a key tumor suppressor gene of mesothelial carcinogenesis. Subclonal tumor populations were shared among paired biopsies, suggesting a polyclonal dissemination of the tumor. Transcriptome analysis highlighted dysregulation of cell adhesion and extracellular matrix pathways, linked to changes in histo-molecular gradient proportions between anatomic sites. Methylome analysis revealed the contribution of epigenetic mechanisms in two patients. Finally, significant changes in the expression of immune mediators and genes related to immunological synapse, as well as differential infiltration of immune populations in the tumor environment, were observed and led to a switch from a hot to a cold immune profile in three patients. Conclusions This comprehensive analysis reveals patient-dependent spatial intra-tumor heterogeneity at the genetic, transcriptomic, and epigenetic levels and in the immune landscape of the tumor microenvironment. Results support the need for multi-sampling for the implementation of molecular-based precision medicine.