Diverse genetic, epigenetic, and developmental programs drive glioblastoma, an incurable and poorly understood tumor, but their precise characterization remains challenging. Here, we use an integrative approach spanning single-cell RNA-sequencing of 28 tumors, bulk genetic and expression analysis of 401 specimens from the The Cancer Genome Atlas (TCGA), functional approaches, and single-cell lineage tracing to derive a unified model of cellular states and genetic diversity in glioblastoma. We find that malignant cells in glioblastoma exist in four main cellular states that recapitulate distinct neural cell types, are influenced by the tumor microenvironment, and exhibit plasticity. The relative frequency of cells in each state varies between glioblastoma samples and is influenced by copy number amplifications of the CDK4, EGFR, and PDGFRA loci and by mutations in the NF1 locus, which each favor a defined state. Our work provides a blueprint for glioblastoma, integrating the malignant cell programs, their plasticity, and their modulation by genetic drivers.

Leptomeningeal metastasis is an uncommon and typically late complication of cancer with a poor prognosis and limited treatment options. Diagnosis is often challenging, with nonspecific presenting symptoms ranging from headache and confusion to focal neurologic deficits, such as cranial nerve palsies. Standard diagnostic evaluation involves a neurologic examination, magnetic resonance imaging of the brain and spine with gadolinium, and cytologic evaluation of the cerebral spinal fluid. Therapy entails a multimodal approach focused on palliation with surgery, radiation, and/or chemotherapy, which may be administered systemically or directly into the cerebral spinal fluid. Limited trial data exist to guide treatment, and current regimens are based primarily on expert opinion. Although newer targeted and immunotherapeutic agents are under investigation and have shown promise, an improved understanding of the biology of leptomeningeal metastasis and treatment resistance as well as additional randomized controlled studies are needed to guide the optimal treatment of this devastating disease. Cancer 2018;124:21‐35. © 2017 American Cancer Society.

Brain metastases from lung adenocarcinoma (BM-LUAD) cause significant patient mortality. To identify genomic alterations that promote brain metastases, we performed whole-exome sequencing of 73 BM-LUAD cases. Using case-control analyses, we discovered candidate drivers of brain metastasis by identifying genes with more frequent copy-number aberrations in BM-LUAD compared to 503 primary lung adenocarcinomas. We identified three regions with significantly higher amplification frequencies in BM-LUAD, including MYC (12% vs 6%), YAP1 (7% vs 0.8%), and MMP13 (10% vs 0.6%) and significantly more frequent deletions in CDKN2A/B (27% vs 13%). We confirmed that amplification frequencies of MYC and YAP1 / MMP13 were elevated in an independent cohort of 105 patients. Functional assessment in patient-derived xenograft mouse models validated that MYC , YAP1 or MMP13 overexpression increased the brain metastasis incidence. These results demonstrate that somatic alterations contribute to brain metastases and that genomic sequencing of a large number of metastatic tumors can reveal novel metastatic drivers.