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Embryonal rhabdomyosarcoma (ERMS) is a devastating cancer with specific features of muscle differentiation that can result from mutational activation of RAS family members. However, to date, RAS pathway activation has not been reported in a majority of ERMS patients. Here, we have created a zebrafish model of RAS-induced ERMS, in which animals develop externally visible tumors by 10 d of life. Microarray analysis and cross-species comparisons identified two conserved gene signatures found in both zebrafish and human ERMS, one associated with tumor-specific and tissue-restricted gene expression in rhabdomyosarcoma and a second comprising a novel RAS-induced gene signature. Remarkably, our analysis uncovered that RAS pathway activation is exceedingly common in human RMS. We also created a new transgenic coinjection methodology to fluorescently label distinct subpopulations of tumor cells based on muscle differentiation status. In conjunction with fluorescent activated cell sorting, cell transplantation, and limiting dilution analysis, we were able to identify the cancer stem cell in zebrafish ERMS. When coupled with gene expression studies of this cell population, we propose that the zebrafish RMS cancer stem cell shares similar self-renewal programs as those found in activated satellite cells.[Keywords: Zebrafish; rhabdomyosarcoma; RAS; P53; transgenic] Supplemental material is available at http://www.genesdev.org.

Osimertinib was initially approved for T790M-positive non-small cell lung cancer (NSCLC) and, more recently, for first-line treatment of -mutant NSCLC. However, resistance mechanisms to osimertinib have been incompletely described. Using cohorts from The University of Texas MD Anderson Lung Cancer Moonshot GEMINI and Moffitt Cancer Center lung cancer databases, we collected clinical data for patients treated with osimertinib. Molecular profiling analysis was performed at the time of progression in a subset of the patients. In the 118 patients treated with osimertinib, 42 had molecular profiling at progression. T790M was preserved in 21 (50%) patients and lost in 21 (50%). EGFR C797 and L792 (26%) mutations were the most common resistance mechanism and were observed exclusively in T790M-preserved cases. MET amplification was the second most common alteration (14%). Recurrent alterations were observed in 22 genes/pathways, including PIK3CA, FGFR, and RET. Preclinical studies confirmed MET, PIK3CA, and epithelial-to-mesenchymal transition as potential resistance drivers. Alterations of cell-cycle genes were associated with shorter median progression-free survival (PFS, 4.4 vs. 8.8 months, = 0.01). In 76 patients with progression, osimertinib was continued in 47 cases with a median second PFS (PFS2) of 12.6 months; 21 patients received local consolidation radiation with a median PFS of 15.5 months. Continuation of osimertinib beyond progression was associated with a longer overall survival compared with discontinuation (11.2 vs. 6.1 months, = 0.02). Osimertinib resistance is associated with diverse, predominantly EGFR-independent genomic alterations. Continuation of osimertinib after progression, alone or in conjunction with radiotherapy, may provide prolonged clinical benefit in selected patients.

Highlights d This large analysis identified ancestry correlates in cancer d Ancestry-associated artifacts and confounders were identified d Ancestry effects are profoundly tissue specific d Rates of FBXW7, VHL, and PBRM1 mutations and immune activity vary by ancestry