ASPSCR1::TFE3 Drives Alveolar Soft Part Sarcoma by Inducing Targetable Transcriptional Programs.

Alveolar soft part sarcoma (ASPS) is a rare mesenchymal malignancy driven by the ASPSCR1::TFE3 fusion. A better understanding of the mechanisms by which this oncogenic transcriptional regulator drives cancer growth is needed to help identify potential therapeutic targets. In this study, we characterized the transcriptional and chromatin landscapes of ASPS tumors and preclinical models, identifying the essential role of ASPSCR1::TFE3 in tumor cell viability by regulating core transcriptional programs involved in cell proliferation, angiogenesis, and mitochondrial biology. ASPSCR1::TFE3 directly interacted with key epigenetic regulators at enhancers and promoters to support ASPS-associated transcription. Among the effector programs driven by ASPSCR1::TFE3, cell proliferation was driven by high levels of cyclin D1 expression. Disruption of cyclin D1/CDK4 signaling led to a loss of ASPS proliferative capacity, and combined inhibition of CDK4/6 and angiogenesis halted tumor growth in xenografts. These results define the ASPS oncogenic program, reveal mechanisms by which ASPSCR1::TFE3 controls tumor biology, and identify a strategy for therapeutically targeting tumor cell-intrinsic vulnerabilities. Significance: The ASPSCR1::TFE3 fusion propels the growth of alveolar soft part sarcoma  by activating transcriptional programs that regulate proliferation, angiogenesis, mitochondrial biogenesis, and differentiation and can be therapeutically targeted to improve treatment.

RAS/RAF Comutation and ERBB2 Copy Number Modulates HER2 Heterogeneity and Responsiveness to HER2-directed Therapy in Colorectal Cancer.

PURPOSE: ERBB2-amplified colorectal cancer is a distinct molecular subtype with expanding treatments. Implications of concurrent oncogenic RAS/RAF alterations are not known. EXPERIMENTAL DESIGN: Dana-Farber and Foundation Medicine Inc. Colorectal cancer cohorts with genomic profiling were used to identify ERBB2-amplified cases [Dana-Farber, n = 47/2,729 (1.7%); FMI, n = 1857/49,839 (3.7%)]. Outcomes of patients receiving HER2-directed therapies are reported (Dana-Farber, n = 9; Flatiron Health-Foundation Medicine clinicogenomic database, FH-FMI CGDB, n = 38). Multisite HER2 IHC and genomic profiling were performed to understand HER2 intratumoral and interlesional heterogeneity. The impact of concurrent RAS comutations on the effectiveness of HER2-directed therapies were studied in isogenic colorectal cancer cell lines and xenografts. RESULTS: ERBB2 amplifications are enriched in left-sided colorectal cancer. Twenty percent of ERBB2-amplified colorectal cancers have co-occurring oncogenic RAS/RAF alterations. While RAS/RAF WT colorectal cancers typically have clonal ERBB2 amplification, colorectal cancers with co-occurring RAS/RAF alterations have lower level ERRB2 amplification, higher intratumoral heterogeneity, and interlesional ERBB2 discordance. These distinct genomic patterns lead to differential responsiveness and patterns of resistance to HER2-directed therapy. ERBB2-amplified colorectal cancer with RAS/RAF alterations are resistant to trastuzumab-based combinations, such as trastuzumab/tucatinib, but retain sensitivity to trastuzumab deruxtecan in in vitro and murine models. Trastuzumab deruxtecan shows clinical efficacy in cases with high-level ERBB2-amplified RAS/RAF coaltered colorectal cancer. CONCLUSIONS: Co-occurring RAS/RAF alterations define a unique subtype of ERBB2-amplified colorectal cancer that has increased intratumoral heterogeneity, interlesional discordance, and resistance to trastuzumab-based combinations. Further examination of trastuzumab deruxtecan in this previously understudied cohort of ERBB2-amplified colorectal cancer is warranted.