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e16507 Background: The phase II BONSAI trial ( n = 25 ; NCT 03354884) met the primary endpoint demonstrating activity of cabozantinib in untreated metastatic collecting ducts carcinoma (mCDC), a rare and biologically poorly characterized disease. Here we report on molecular analyses of baseline tissue samples. Methods: Formalin-fixed paraffin-embedded (FFPE) samples from 18 mCDC patients enrolled in BONSAI were sequenced by TruSeq RNA Exome kit (Illumina). The data were mapped and quantified using STAR and htseq, respectively. Globaltest and edgeR packages in R were used to assess the correlation between transcriptional profiles and survival data. Nineteen samples underwent DNA Sequencing with the Oncomine Comprehensive Assay Plus (ThermoFisher Scientific). The reads were aligned to the human genome reference (hg19) and analyzed with Opencravat and IonReporter software. Germline variants were excluded based on 1000 Genomes, GnomAd and Exac databases, and Clinical annotation of somatic variants was performed using ClinVar. Results: The global expression levels of thirty-one genes have been found significantly associated with overall survival (OS). The natural grouping of the 18 tumor samples based on the 31-gene signature identified a main group of 11 cases, showing global higher expression levels in 22 out of the 31 genes. This group displayed overall a significant higher OS rate in comparison to the remaining 7 patients, carrying opposite expression trend and mostly undergoing to disease progression. The identified signature was enriched in biological processes like cell junction, cytoskeleton organization and methylation. FOS oncogene was among the 9 genes negatively associated to OS, showing common higher expression in the poorer survival rate group. Furthermore, a 22-gene signature was found significantly associated with progression-free survival (PFS), involving mainly genes associated to cell cycle regulation or recognized as components of Golgi apparatus. Only three genes were globally up-regulated in the group of 9 patients characterized by shorter PFS. Finally, heterogeneous pattern of somatic mutations was identified in 19 tumor samples, with at least 8 genes recurrently affected in more than three patients. Notably, mutated genes were mostly involved in DNA repair and chromatin modification processes. Conclusions: Our findings for the first time define specific molecular signatures that differentiate therapy-specific outcomes in first-line mCDC, warranting further investigation of their involvement in the tumor biology. Clinical trial information: NCT 03354884.

4571 Background: Metastatic collecting ducts carcinoma (mCDC) is a rare disease with bad prognosis and no standard treatments. Due to its rarity, mCDC is biologically poorly characterized and under-represented in prospective randomized trials. We recently identified two different molecular subtypes of mCDC based on relative expression levels of angiogenesis, metabolic and immune-related genes. Methods: : This prospective, monocentric, phase II trial evaluated cabozantinib (cabo) 60 mg orally once daily until progression or unacceptable toxicity in untreated mCDC patients (pts). Primary endpoint was objective response rate (ORR) as the proportion of pts with best overall response of confirmed complete (CR) or partial responses (PR) per RECIST 1.1. Secondary endpoints were progression-free survival (PFS), overall survival and safety profile. Exploratory objectives were: to identify somatic mutations by targeted NGS-based sequencing; to define molecular subtypes, signatures and transcript fusions genes by RNA sequencing; to monitor circulating immune cells and study the immunological context of tumor cells. A central pathological review was mandatory. The study was based on a Simon’s two stage optimal design: at least 2 responses in 9 pts in the first stage were needed to proceed to the second stage where at least 6 responses in 14 additional pts were needed to prove activity of cabo. Results: From January 2018 to November 2020, 25 pts were enrolled, of whom 23 started treatment. Median age was 66 years, 19 pts were male. 19 (83%) pts received a previous nephrectomy. 9 pts presented with only one metastatic site, 8 pts with two, while the remaining part with multiple sites. The most common metastatic sites were lymphnodes and bone (15 and 13 pts respectively), followed by lung and liver (10 and 4 pts respectively). Median follow up was 8 months. As best overall response, 6 pts presented a stable disease (26%),1 pt achieved a confimed CR and 7 a PR for an ORR of 35%. Median PFS was 6 months. Treatment was feasible and well tolerated. All pts reported at least one grade (G) 1-2 adverse event (AE): the most common were fatigue (43%), hypotiroidism (28%), stomatitis (28%), anorexia (26%), Hand-Foot Syndrome (13%), hypertension (17%), and diarrhea (13%). 5 pts reported G3 AEs (2 thromboembolic events, 2 arterial hypertension, 1 fatigue), while no G4-5 AEs were reported. 17% of pts required dose reduction. DNA sequencing on CDC showed to be feasible, finding 256 mutations in 119 genes (missens mutations the majority). Altered genes, molecular subtypes and signatures will be associated to different outcomes and responses to cabo. Conclusions: The study met its primary endpoint showing promising efficacy and acceptable tolerability of cabo in mCDC pts. Mature results according to mutational profiles and gene signatures will be presented. Clinical trial information: NCT03354884.

714 Background: Collecting duct carcinoma is a rare, highly aggressive and molecularly uncharacterized kidney disease with poor outcome. To date, no standard therapies are available and treatment choice is based on retrospective data. Identifying molecular features of this tumor could provide a biologic rationale for novel targeted systemic therapies. Methods: Total RNA was extracted from formalin-fixed paraffin-embedded (FFPE) tissues of 6 CDCs, 5 clear cell renal carcinomas (ccRCCs) and 4 adjacent normal tissues. Samples were profiled by GeneChip Human Transcriptome Array 2.0 (Affymetrix) and constituted the Istituto Nazionale dei Tumori (INT) dataset. Data were pre-processed using the robust multi-array average method and differentially expressed genes were identified according to the limma pipeline. Genes with a false discovery rate < 0.25 were selected. Pathway analysis was performed by gene set enrichment analysis (GSEA), single sample (ss) GSEA, DAVID Bioinformatics Resources 6.8 and Pathfinder Bioconductor package. Moreover, a list of genes representing angiogenesis and immune biology, previously used in the IMmotion150 study, was chosen to explore further functional subcategories of CDC. Available RNA-Seq data of 7 CDCs and 5 matched normal tissue from GSE89122 dataset were used for validation. Results: Comparison of transcriptome profiles of CDCs and ccRCCs versus normal tissue led to the identification of a core of 14 genes specifically up-regulated in CDC, 5 of which (SFN, S100A11, CKAP5, CDH1 and CD44) were significantly involved in extracellular matrix organization. Other deregulated genes were related to immune system, cell cycle progression, glucose and pentose phosphate metabolism and EGFR-signaling. In addition, ssGSEA permitted to identify two major distinct biological subgroups in CDC of both INT and GSE89122 datasets, based on relative expression levels of angiogenesis and immune genes. Conclusions: Our study reveals novel insights into the biology and heterogeneity of CDCs. Although further validation using larger samples is needed, the current findings suggest that this heterogeneity could have clinical implications for the treatment of patients with this rare kidney cancer.