AIMS:Leiomyomas (LM) are the most common uterine mesenchymal neoplasms and encompass a variety of histological subtypes. Bizarre nuclei are described in both leiomyomas with bizarre nuclei (LM-BN) and fumarate hydratase-deficient leiomyomas (FH-LM), which raise diagnostic concerns regarding leiomyosarcoma (LMS). Recently, an immunohistochemical algorithm to support the diagnosis of LMS based on the genomic landscape of these neoplasms was proposed. This study aimed to evaluate the algorithm's accuracy in distinguishing LM-BN and FH-LM from LMS. METHODS AND RESULTS:We collected 68 LM (29 LM-BN, 30 FH-LM, and 9 LM) and 9 LMS, along with clinicopathological and molecular data. An immunohistochemical panel comprising p53, Rb, PTEN, ATRX, DAXX, and MDM2 was applied. Nine cases were non-interpretable due to fixation issues. The algorithm demonstrated 100% accuracy for LM without bizarre nuclei (9/9) and for nonmyxoid LMS (5/5). Notably, 28.6% (14/49) of LM-BN and FH-LM exhibited at least two abnormalities, leading to potential misclassification as LMS. However, their clinical course, morphology, and genomic profile supported a benign diagnosis. Frequent alterations included Rb (20/49; 40.8%) and p53 (19/49; 38.8%), particularly in bizarre cells, while no abnormal staining was observed for ATRX, DAXX, or MDM2. CONCLUSION:The proposed algorithm has limitations in differentiating LMS from LM-BN and FH-LM, misclassifying 28.6% of the latter. Accurate interpretation requires proper internal controls, particularly for markers whose loss of expression favours malignancy. Morphology remains central for diagnosis, although integration of molecular data may provide additional insights for a definitive classification in challenging cases.

Purpose: Molecular profiling is increasingly implemented to guide treatment of advanced pancreatic ductal adenocarcinoma (PDAC), especially when for clinical trials enrollment. This study aimed to describe actionable alterations detected in KRAS mutated (KRASm) versus KRAS wild-type (KRASwt) PDAC, the latter group being considered enriched in molecular alterations. Methods: This prospective monocentric study included patients with locally advanced or metastatic PDAC who underwent next-generation sequencing (NGS) on liquid biopsy and/or tissue samples between 2015 and 2023, as part of the BIP academic study (NCT02534649). Actionable alterations were classified using the ESCAT (ESMO Scale for Clinical Actionability of molecular Targets). Results: A total of 378 patients with a PDAC underwent NGS: 73 on tissue samples, 162 on liquid biopsies, and 143 on both tissue and liquid. Liquid biopsies had a 59.3 % performance (181 informative samples out of 305). Among 318 informative NGS samples, 273 (86 %) were KRASm, and 45 (14 %) were KRASwt. Median overall survival (OS) was 19.35 in KRASwt patients and 16.89 months for KRASm patients (HR 0.67, 95 %CI (0.49-0.90), p = 0.02). ESCAT alterations were found in 15.7 % of total population, with 31.1 % in KRASwt tumors and 13.2 % in KRASm tumors. BRCA1/2 mutations were identified in 7.5 % of the population, and one NTRK fusion was found in a KRASwt PDAC. The molecular tumor board considered 71 patients (22.3 %) eligible for earlyphase trials, with 14 treated with matched therapy. Conclusion: Although actionable mutations were more frequent in KRASwt tumors, 13.2 % of KRASm PDAC harbored ESCAT alterations, emphasizing the importance of molecular profiling regardless of KRAS status.

Selecting patients for phase I cancer trials is crucial to ensure a sufficient life expectancy. Frail patients, better suited for palliative care, should not be exposed to new drugs with minimal benefit. Enrolling patients at high risk of early death can jeopardize the study. Our analysis of two large precision medicine studies used tumor fraction from ctDNA to develop a predictive model, demonstrating notable predictive accuracy and aiding in patient selection.

Radiomics has traditionally focused on individual tumors, often neglecting the integration of metastatic disease, particularly in patients with non-small cell lung cancer. This study sought to examine intra-patient inter-tumor lesion heterogeneity indices using radiomics, exploring their relevance in metastatic lung adenocarcinoma. Consecutive adults newly diagnosed with metastatic lung adenocarcinoma underwent contrast-enhanced CT scans for lesion segmentation and radiomic feature extraction. Three methods were devised to measure distances between tumor lesion profiles within the same patient in radiomic space: centroid to lesion, lesion to lesion, and primitive to lesion, with subsequent calculation of mean, range, and standard deviation of these distances. Associations between HIs, disease control rate, objective response rate to first-line treatment, and overall survival were explored. The study included 167 patients (median age 62.3 years) between 2016 and 2019, divided randomly into experimental (N = 117,546 lesions) and validation (N = 50,232 tumor lesions) cohorts. Patients without disease control/objective response and with poorer survival consistently systematically exhibited values of all heterogeneity indices. Multivariable analyses revealed that the range of primitive-to-lesion distances was associated with disease control in both cohorts and with objective response in the validation cohort. This metrics showed univariable associations with overall survival in the experimental. In conclusion, we proposed original methods to estimate the intra-patient inter-tumor lesion heterogeneity using radiomics that demonstrated correlations with patient outcomes, shedding light on the clinical implications of inter-metastases heterogeneity. This underscores the potential of radiomics in understanding and potentially predicting treatment response and prognosis in metastatic lung adenocarcinoma patients.

Atypical spindle cell/pleomorphic lipomatous tumor (ASPLT) is a recently described adipocytic tumor predominantly affecting the subcutaneous soft tissues of adults. Previous studies have shown that ASPLT follows a benign clinical course with a 4% to 12% local recurrence rate and no risk of dedifferentiation. Herein, we describe the clinicopathologic and molecular findings of 4 cases of ASPLT showing unequivocal sarcomatous transformation. Three patients were male and one was female, aged 65, 70, 74, and 78 years. Two cases presented as mass-forming lesions, while 1 case was incidentally discovered. The tumors measured 30, 55, 80, and 110 mm and occurred in the chest wall (n = 2) or arm (n = 2); all were subcutaneous. Microscopically, they showed a biphasic appearance comprising a low-grade ASPLT component and a high-grade sarcomatous component. The low-grade components showed features in the spectrum of either atypical pleomorphic lipomatous tumor (n = 2) or atypical spindle cell lipomatous tumor (n = 2). The high-grade components displayed leiomyosarcoma-like (n = 2), pleomorphic liposarcoma-like (n = 1) or undifferentiated sarcoma-like (n = 1) morphology. On immunohistochemistry, tumors were negative for MDM2 and showed loss of RB1 expression. In addition, the leiomyosarcoma-like areas seen in 2 cases were positive for smooth muscle actin and H-caldesmon. Single-nucleotide polymorphism array, performed in 3 cases, showed deletions of TP53, RB1, and flanking genes in both components. In contrast, the sarcomatous components showed more complex genomic profiles with rare segmental gains and recurrent loss of PTEN (n = 3), ATM (n = 2), and CDKN2A/B (n = 2) among other genes. Whole exome sequencing identified a TP53 variant in one case and an ATRX variant in another, each occurring in both tumor components. Limited clinical follow-up showed no recurrence or metastasis after 1 to 13 months (median, 7.5 months) postsurgical excision. Altogether, our data support that ASPLT can rarely develop sarcomatous transformation and offer insights into the molecular mechanisms underlying this event.

A close relationship has been demonstrated between genomic complexity and clinical outcome in uterine smooth muscle tumors. We studied the genomic profiles by array-CGH of 28 fumarate hydratase deficient leiomyomas and 37 leiomyomas with bizarre nuclei (LMBN) from 64 patients. Follow-up was available for 46 patients (from three to 249 months, mean 87.3 months). All patients were alive without evidence of disease. For 51 array-CGH interpretable tumors the mean Genomic Index (GI) was 16.4 (median: 9.8; from 1 to 57.8), significantly lower than the mean GI in LMS (mean GI 51.8, p < 0.001). We described three groups: (1) a group with FH deletion (24/58) with low GI (mean GI: 11 vs. 22,4, p = 0.02), (2) a group with TP53 deletion (17/58) with higher GI (22.4 vs. 11 p = 0.02), and (3) a group without genomic events on FH or TP53 genes (17/58) (mean GI:18.3; from 1 to 57.8). Because none of these tumors recurred and none showed morphological features of LMS we concluded that GI at the cut-off of 10 was not applicable in these subtypes of LM. By integration of all those findings, a GI <10 in LMBN remains a valuable argument for benignity. Conversely, in LMBN a GI >10 or alteration in tumor suppressor genes, should not alone warrant a diagnosis of malignancy. Nine tumors were tested with Nanocind CINSARC® signature and all were classified in low risk of recurrence. We propose, based on our observations, a diagnostic approach of these challenging lesions.

Abstract Modern phase I trials have shown considerable advancement, demonstrating encouraging response rates and subsequently raising the demand for participant enrollment. Despite these advances, there remains a significant challenge: approximately 15% of patients enrolled in these trials pass away within the first 90 days, and nearly half of them do not experience any therapeutic benefit. These statistics underscore the critical need for more effective strategies in selecting suitable patients for trial participation. One promising avenue is the use of circulating tumor DNA (ctDNA) measurements to estimate tumor fraction (TF), a method that has shown potential in prognosticating outcomes for patients with solid tumors. Nevertheless, the effectiveness of TF as an indicator for predicting the clinical benefits of systemic treatments in patients referred for early phase studies is yet to be conclusively determined Methods: We analyzed adult patients with advanced solid tumors included from December 2020 to December 2021 in two precision medicine studies: BIP (NCT02534649) and STING (NCT04932525). Comprehensive genomic profiling was conducted using the FDA approved 324-gene FoundationOne Liquid Cdx assay. TF was categorized as ≥10% or <10%. Multivariate analysis incorporated established prognostic scores (Royal Marsden Hospital: RMH, Garrido-Laguna et al. 2012; and GRIm, Bigot et al., 2017) and their individual components (RMH: albumin, lactate dehydrogenase, number of metastatic sites; GRIm: neutrophil/lymphocyte ratio, lactate dehydrogenase, albumin). Results: A total of 1305 patients referred for early phase trials were evaluated: 871 in BIP and 434 in STING.The treatment regimens patients received post-TF assessment included: cytotoxic agents (BIP: 278 patients, 28.8%; STING: 106 patients, 24.4%), immunotherapy (BIP: 152 patients, 15.8%; STING: 76 patients, 17.5%), tyrosine kinase inhibitors (BIP: 126 patients, 13.1%; STING: 35 patients, 8.1%), hormonal therapy (BIP: 131 patients, 13.6%; STING: 9 patients, 2.1%), and various other therapies or combinations. High TF was significantly correlated with poorer objective response/stable disease rate, shorter progression-free survival (PFS), and lower overall survival (OS) in both studies. Multivariate analysis confirmed TF as an independent predictor of objective response, PFS, and OS, beyond the RMH and GRIm scores and their components. Conclusions: This is the first prospective analysis confirming that TF is a significant predictive marker of treatment efficacy in patients referred for early phase studies. Our findings suggest that TF could be a valuable tool in decision-making for phase I trial participation. Additionally, this research lays the groundwork for future exploration of TF in risk stratification of cancer patients in various clinical contexts. Citation Format: Laila Belcaid, Sophie Cousin, Arnaud Bayle, Melissa Alame, Etienne Rouleau, Laura Blouin, Ludovic Lacroix, Damien Vasseur, Maxime Brunet, Sofiane Taleb, Isabelle Soubeyran, Veronique Debien, Eurydice Angeli, Christophe Massard, Antoine Italiano. Tumor fraction as a predictive factor of outcome in patients referred for oncology early phase clinical trials: Analyses of two precision medicine studies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB104.

We report the first two cases of EGFR exon20ins SCLC, treated with amivantamab and TKIs.

Background Despite the effectiveness of the various targeted therapies currently approved for solid tumors, acquired resistance remains a persistent problem that limits the ultimate effectiveness of these treatments. Polyclonal resistance to targeted therapy has been described in multiple solid tumors through high-throughput analysis of multiple tumor tissue samples from a single patient. However, biopsies at the time of acquired resistance to targeted agents may not always be feasible and may not capture the genetic heterogeneity that could exist within a patient. Methods We analyzed circulating tumor DNA (ctDNA) with a large next-generation sequencing panel to characterize the landscape of secondary resistance mechanisms in two independent prospective cohorts of patients (STING: n = 626; BIP: n = 437) with solid tumors who were treated with various types of targeted therapies: tyrosine kinase inhibitors, monoclonal antibodies and hormonal therapies. Results Emerging alterations involved in secondary resistance were observed in the plasma of up 34% of patients regardless of the type of targeted therapy. Alterations were polyclonal in up to 14% of patients. Emerging ctDNA alterations were associated with significantly shorter overall survival for patients with some tumor types. Conclusion This comprehensive landscape of genomic aberrations indicates that genetic alterations involved in secondary resistance to targeted therapy occur frequently and suggests that the detection of such alterations before disease progression may guide personalized treatment and improve patient outcome.

3005 Background: Typical entry criteria in early phase studies include expected life expectancy greater than 3 months. However, this evaluation is quite subjective and more objective and reproducible tools are needed to improve patients (pts) selection. The quantification of ctDNA shed by measuring tumor fraction (TF) has been associated with prognosis in solid tumors pts. However, prognostic implications of TF quantification have been evaluated primarily in retrospective studies and in a limited number of cancer types. We report here the first prospective evaluation of the prognostic impact of TF in 2 independent precision medicine studies enrolling pts referred to consider their eligibility to early phase trials. Methods: All consecutive adult pts with an advanced solid tumor included between December 2020 and December 2021 in 2 precision medicine studies: BIP (NCT02534649, sponsor: Institut Bergonié, Bordeaux, France) and STING (NCT04932525, sponsor: Institut Gustave Roussy, Villejuif, France). All pts underwent comprehensive genomic profiling with the 324-gene FoundationOne. TF was analyzed as a binary variable, indicating whether a specimen had TF ≥10% or TF <10%. Multivariate analysis included previously validated prognostic scores: the Royal Marsden Hospital (albumin, LDH, number of metastatic sites) and the GRIm (LDH, neutrophil/lymphocyte ratio (NLR), albumin) scores as well as their individual components. Results: 1912 pts: N=965 in BIP and N=947 in STING were included. Their characteristics are described. High TF was associated with significantly worse overall survival (OS) in both BIP and STING studies. On multivariate analysis, TF was associated with worse OS (HR:2.49 [CI95%: 2.11 - 2.95, p<0.001] and HR:2.52 [CI95%: 2.06 - 3.08, p<0.001] in BIP and STING studies respectively) independently of the RMH and GRIM scores as well as their individual components. Conclusions: This is the first prospective analysis confirming that TF is a strong prognostic factor in pts with advanced solid tumors and represent an helpful tool in the process of patient selection for phase I trial entry. [Table: see text]

Adult granulosa cell tumor is the most common malignant ovarian sex cord-stromal tumor and heterologous elements, in the form of hepatocytes or mucinous epithelium, have rarely been described in these neoplasms. Here, we report an adult granulosa cell tumor in a 61-year-old woman with classic and luteinized elements and exhibiting a previously unreported feature in the form of foci of mature adipocytes. In reporting this case, we review heterologous adipocytic elements and other heterologous elements in ovarian sex cord-stromal tumors and speculate on the pathogenesis of the adipocytic differentiation.

DICER1-mutated rhabdomyosarcoma is a rare, emerging entity with a predilection for the gynecologic and genitourinary tracts. We report here a case of DICER1-mutated rhabdomyosarcoma of the ovary in a 14 years old girl which displayed interspersed mature teratoid glands, neuroectodermal rosettes and immature blastematous-like tubes. Morphologically the sarcomatous component predominated, corresponding to a high grade spindle cell rhabdomyosarcoma with botryoid features. Islets of cartilage were present. The sarcomatous proliferation encased the teratoid glands, forming cambium layer-like arrangements. The sarcoma cells were Myogenin and MYOD1 positive, the neuroectodermal rosettes expressed SALL4 along with cytokeratins and EMA and were negative for Inhibin; immature blastematous-like tubes were negative for SALL4 and Inhibin. Whole RNA- and targeted DNA-sequencing revealed two DICER1 mutations in exon 26: c.5113G>A: p.(Glu1705Lys) and exon 12: c.1642C>T: p.(Gln548X). The sarcomatous component harbored a complex genetic profile while the teratoid component was diploid, none of the above displayed abnormality of 12p. DICER1-mutated sarcomas display pathological features similar to embryonal rhabdomyosarcomas, botryoid type. They also display heterogeneous features combining cartilage foci, teratoid mature glands, immature blastematous-like tubes and/or neuroectodermal components. Molecular testing remains necessary to confirm the diagnosis. Further studies need to clarify the nosology of DICER1-mutated sarcomas and devise specific therapeutic strategies.

Imaging can capture phenotypic intra- and inter-tumoral heterogeneities. Radiomics provides a radiophenotypic quantification but has mostly focused on single tumors, letting apart metastatic patients. Our aim was to develop inter-site heterogeneity indices (ISHIs) using radiomics and to investigate their predictive value regarding treatment response and overall survival (OS) in lung adenocarcinoma patients. All measurable target lesions per RECIST with volume>1cm3 from consecutive adult patients with newly-diagnosed metastatic lung adenocarcinoma were segmented on contrast-enhanced CT-scan to extract 121 3D-radiomics features (RFs). Four methods were developed to quantify the dissimilarity (Ds) between the lesion profiles from a same patient in the radiomics space, namely: Centroid-to-Lesion (CL), Lesion-to-Lesion (LL), Primitive-to-Lesion (PL) - followed by mean, range and standard deviation (SD) of those distances -, and using clustering to define lesion groupings and calculating grouping diversity with Shannon Entropy (SE). Associations between the 10 resulting ISHIs and disease control rate (DCR), objective response rate (ORR) to first-line treatment and OS were investigated in univariate and stepwise multivariate analyses including cofounding variables (performance status, sex, age, staging, number of metastatic sites, liver and bone metastases). 167 patients (62 women, median age: 62.3 years) were included between 2016 and 2019, and randomly separated into one experimental (N=117 [70%], 546 lesions) and one validation (N=50 [30%], 232 lesions) cohorts. Higher ISHIs were systematically found in patients without disease control, without objective response and with worse OS. Range(Ds-PL) was independently associated with DCR in both cohorts (odds ratio [OR]=1.30, P=0.02 and OR=1.50, P=0.02, respectively). Range(Ds-PL) was independently associated with ORR in the validation cohort (OR=1.46, P=0.049 versus OR=1.23, P=0.055 in the experimental cohort). SE was independently correlated with OS in the experimental cohort (hazard ratio [HR]=2.39, P=0.005) whereas Range(Ds-PL) was selected in the last regression step in the validation cohort (HR=1.16, P=0.08). None of the ISHIs was associated with PD-L1 status; however, trend towards lower ISHI values were observed in EGFR, ALK and ROS1 altered tumors versus the others. Radiomics-based ISHIs were associated with ORR, DCR and OS and appeared as promising metrics to deepen our understanding of the clinical implication of intra-patient inter-tumor heterogeneity. Correlation assessment between radiomics-based ISHIs and tumor heterogeneity evaluated by a baseline ctDNA profiling (FondationOne® Liquid CDx) before treatment in metastatic lung adenocarcinoma patients is ongoing and will be presented. Citation Format: Mathilde Lafon, Sophie Cousin, Mélissa Alamé, Michèle Kind, Antoine italiano, Amandine Crombé. Predictive value of baseline inter-sites heterogeneity measured by radiomics in metastatic lung adenocarcinomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 863.

11550 Background: Preliminary studies have suggested that the detection, quantification, and profiling of ctDNA in patients with sarcoma is feasible and may improve prognostication, measure treatment response, and detect relapse. However, data related to impact of ctDNA profiling to tailor therapy in patients with advanced disease are lacking. Methods: Patients with advanced soft-tissue sarcomas (STS) have been included in two ongoing institutional molecular profiling studies (BIP: NCT02534649, STING: NCT04932525). Genomic analysis (ctDNA in all cases and tissue when available) was performed by using the Foundation One Liquid CDx Assay (324 genes, tumor mutational burden [TMB], microsatellite instability status). Each individual genomic report was reviewed and discussed weekly by a multidisciplinary tumour board dedicated to precision medicine, attended by experts in clinical oncology, molecular biology, and clinical genetics. Actionable targets were defined by the MTB according to the existing level of evidence (ESCAT), and molecular-based treatment suggestions were proposed where possible. Results: Between December 2020 and August 2021, 98 patients with metastatic STS underwent ctDNA profiling. Median time to assay results was 12 days. Results were contributive for 86 patients (88%). At least one actionable target (range 1-4) was detected in 35 patients (36%) including high tumor mutational burden (> 16 mutations/Mb) for 1 patient (1%) and alteration of the DNA repair response pathway for 12 patients (12%). Overall, the MTB recommended a matched therapy for 27 patients (28%). 40 patients underwent also NGS of tissue besides ctDNA profiling. The number of actionable alterations was similar in 26 (65%), whereas it was higher in tissue for 10 (25%) and in liquid for 4 (10%) patients. Conclusions: This large-scale study demonstrates that liquid biopsy with a large NGS ctDNA panel is an efficient approach to match patients to genomically directed clinical trials/targeted therapies in patients with advanced STS. Outcomes of patients treated with matched therapy will be presented at the meeting.

Neoplasms harboring a KAT6B/A::KANSL1 fusion were initially reported as benign (leiomyomas) and malignant (leiomyosarcomas, low-grade endometrial stromal sarcomas [LG-ESSs]) uterine neoplasms. However, they may represent an emerging entity characterized by clinical aggressiveness contrasting with a rather reassuring microscopic appearance. Here, we aimed to confirm that this neoplasm is a distinct clinicopathologic and molecular sarcoma and identify criteria that should alert pathologists and lead to KAT6B/A::KANSL1 fusion testing in routine practice. Therefore, we conducted a comprehensive clinical, histopathologic, immunohistochemical, and molecular study, including array comparative genomic hybridization, whole RNA-sequencing, unsupervised clustering, and cDNA mutational profile analyses of 16 tumors with KAT6B::KANSL1 fusion from 12 patients. At presentation, patients were peri-menopausal (median, 47.5 years), and the primary tumors were located in the uterine corpus (12/12, 100%), with an additional prevesical location in 1 (8.3%) of 12 cases. The relapse rate was 33.3% (3/9). All tumors (16/16, 100%) showed morphologic and immunohistochemical features overlapping between leiomyoma and endometrial stromal tumors. A whirling recurrent architecture (resembling fibromyxoid-ESS/fibrosarcoma) was found in 13 (81.3%) of 16 tumors. All tumors (16/16, 100%) exhibited numerous arterioliform vessels, and 13 (81.3%) of 18 had large hyalinized central vessels and collagen deposits. Estrogen and progesterone receptors were expressed in 16 (100%) of 16 and 14 (87.5%) of 16 tumors, respectively. Array comparative genomic hybridization performed on 10 tumors classified these neoplasms as simple genomic sarcomas. Whole RNA-sequencing on 16 samples and clustering analysis on primary tumors found that the KAT6B::KANSL1 fusion always occurred between exons 3 of KAT6B and 11 of KANSL1; no pathogenic variant was identified on cDNA, all neoplasms clustered together, close to LG-ESS, and pathway enrichment analysis showed cell proliferation and immune infiltrate recruitment pathway involvement. These results confirm that the sarcomas harboring a KAT6B/A::KANSL1 fusion represent a distinct clinicopathologic entity, close to LG-ESS but different, with clinical aggressiveness despite a reassuring morphology, for which the KAT6B/A::KANSL1 fusion is the molecular driver alteration.

Systemic mastocytosis is characterised by tissular infiltration and a cytokine storm due to mast cells excessive proliferation and activation. Herein, we report an extraordinary case of AH1N1 influenza post-viral glomerulonephritis occurring in the course of an aggressive systemic mastocytosis with an associated hematological neoplasm. Because of a multisystemic involvement including the liver and lungs, we treated mastocytosis with midostaurin (multiple inhibitor of kinase protein), anti H1/H2 blockers and dexamethasone as first line treatment. One month later and despite vaccination, he developed a severe acute lung injury with respiratory distress due to AH1N1 influenza in association with the nephrotic syndrome. Kidney biopsy disclosed a membranoproliferative glomerulonephritis that was successfully treated with mycophenolate mofetil. Only a few cases of influenza post-viral or post-vaccination glomerulonephritis are documented in the medical literature. This is an exceptional association of uncommon conditions occurring within only a few months in the same patient.

3016 Background: Despite the effectiveness of the various targeted therapies currently approved in solid tumors, acquired resistance remains a persistent problem that limits the ultimate effectiveness of these treatments. Polyclonal resistance to targeted therapy has been described in multiple solid tumors through high throughput analysis of multiple tumor tissue samples from a single patient. However, biopsies at the time of acquired resistance to targeted agents may not always be feasible and may not capture the genetic heterogeneity that could exist within a patient. We used here sequencing of circulating tumor DNA (ctDNA) to characterize the landscape of secondary resistance mechanisms in a large cohort of patients with solid tumors. Methods: This study enrolled patients with advanced cancer from two institutional molecular profiling program STING (NCT04932525, sponsor: Gustave Roussy) or BIP (NCT02534649sponsor: Institut Bergonié). Genomic analysis was performed for each patient by using the Foundation One Liquid CDx Assay (324 genes, tumor mutational burden [TMB], microsatellite instability status). Results: 3435 patients with metastatic disease entered the study. Among them 992 patients (29%) received a targeted therapy matched to a specific molecular alteration before ctDNA. The main tumor types were: prostate cancer (349, 35%), luminal breast cancer (236, 24%), oncogene-addicted non-small cell lung cancer (129, 13%), KRAS-wild type colorectal cancer (126, 13 %). The most frequent class of targeted agents were androgen receptor pathway inhibitor (n = 350, 35%), aromatase inhibitor (236, 24%), anti- EGFR monoclonal antibodies (166, 17%), anti- EGFR tyrosine kinase inhibitors (83, 8%). ctDNA sequencing revealed DNA aberrations involved in secondary resistance in 308 patients (31%). The most frequent aberrations were AR mutations/amplifications, ESR1 point mutations, KRAS point mutations, EGFR point mutations. Among patients with resistance mutation, polyclonal aberrations were identified in 123 patients (40%). The median number of polyclonal aberrations per patient was 2 (range: 2-16). Polyclonal aberrations involved at least 2 different genes in 32 patients (10%). Preliminary results suggest that patients with polyclonal aberrations had worse outcome in comparison with patients with one or no detected aberration and final data will be presented at the time of the congress. Conclusions: We report here the first comprehensive landscape of genomic aberrations in ctDNA involved in resistance to targeted therapies in cancer patients. Polyclonal secondary genomic aberrations represent a frequent clinical resistance mechanism that may explain the poor rate of sustained complete remission observed with targeted therapies and must guide the development of future combinatorial strategies.

Aims Diffuse large B-cell lymphoma (DLBCL) is the most common type of aggressive non-Hodgkin's lymphoma that represents a heterogeneous group of disease that is differentially characterised by clinical, molecular and cytogenetic features. MYC , BCL2 and BCL6 gene rearrangements have been identified as prognostic factors in DLBCL, especially for MYC . Nevertheless the frequency and effect of atypical/unbalanced BCL6, BCL2 and MYC translocations in DLBCL is not fully documented. Here, we aimed to analyse those atypical/unbalanced rearrangements in DLBCL and to assess their prognostic impact. Methods We collected tumour tissue and clinical data from 97 DLBCL and used interphase fluorescence in situ hybridisation (FISH) with break-apart probe to characterise BCL6, BCL2 and MYC gene pattern. Results 19 of 97 (19,6%) cases of DLBCL had atypical/ unbalanced gene rearrangements (14 involving BCL6 gene, 5 involving BCL2 gene and none involving MYC gene). Compared with patients with simple gene rearrangement and patients without cytogenetic abnormality, patients with atypical/unbalanced gene rearrangement were in an unfavourable risk group by the International Prognostic Index (p=0039), died of disease (p=0012), harboured relapse or progression (p=0011) and had shorter overall (p=0,04), relapse free (p=0029) and event free (p=0026) survival. Conclusions We showed that patients with DLBCL with BCL2 or BCL6 atypical/unbalanced rearrangements constituted a group of patients with poor outcome. We also underlined the importance of FISH analyses, easily feasible in routine practise, at diagnosis of DLBCL to detect the rather frequent and clinically significant atypical/unbalanced aberrations of these genes.

Rationale: Primary central nervous system diffuse large B-cell lymphoma (PCNSL) is a rare and aggressive entity that resides in an immune-privileged site. The tumor microenvironment (TME) and the disruption of the immune surveillance influence lymphoma pathogenesis and immunotherapy resistance. Despite growing knowledge on heterogeneous therapeutic responses, no comprehensive description of the PCNSL TME is available. We hence investigated the immune subtypes of PCNSL and their association with molecular signaling and survival. Methods: Analysis of PCNSL transcriptomes (sequencing, n = 20; microarrays, n = 34). Integrated correlation analysis and signaling pathway topology enabled us to infer intercellular interactions. Immunohistopathology and digital imaging were used to validate bioinformatic results. Results: Transcriptomics revealed three immune subtypes: immune-rich, poor, and intermediate. The immune-rich subtype was associated to better survival and characterized by hyper-activation of STAT3 signaling and inflammatory signaling, e.g., IFNγ and TNF-α, resembling the hot subtype described in primary testicular lymphoma and solid cancer. WNT/β-catenin, HIPPO, and NOTCH signaling were hyper-activated in the immune-poor subtype. HLA down-modulation was clearly associated with a low or intermediate immune infiltration and the absence of T-cell activation. Moreover, HLA class I down-regulation was also correlated with worse survival with implications on immune-intermediate PCNSL that frequently feature reduced HLA expression. A ligand-receptor intercellular network revealed high expression of two immune checkpoints, i.e., CTLA-4/CD86 and TIM-3/LAGLS9. TIM-3 and galectin-9 proteins were clearly upregulated in PCNSL. Conclusion: Altogether, our study reveals that patient stratification according to immune subtypes, HLA status, and immune checkpoint molecule quantification should be considered prior to immune checkpoint inhibitor therapy. Moreover, TIM-3 protein should be considered an axis for future therapeutic development.