Ever since Stephen Paget’s 1889 hypothesis, metastatic organotropism has remained one of cancer’s greatest mysteries. Here we demonstrate that exosomes from mouse and human lung-, liver- and brain-tropic tumour cells fuse preferentially with resident cells at their predicted destination, namely lung fibroblasts and epithelial cells, liver Kupffer cells and brain endothelial cells. We show that tumour-derived exosomes uptaken by organ-specific cells prepare the pre-metastatic niche. Treatment with exosomes from lung-tropic models redirected the metastasis of bone-tropic tumour cells. Exosome proteomics revealed distinct integrin expression patterns, in which the exosomal integrins α6β4 and α6β1 were associated with lung metastasis, while exosomal integrin αvβ5 was linked to liver metastasis. Targeting the integrins α6β4 and αvβ5 decreased exosome uptake, as well as lung and liver metastasis, respectively. We demonstrate that exosome integrin uptake by resident cells activates Src phosphorylation and pro-inflammatory S100 gene expression. Finally, our clinical data indicate that exosomal integrins could be used to predict organ-specific metastasis.

The oncogenic mechanisms underlying acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA; 15-39 years old) remain largely elusive. Here we have searched for new oncogenes in AYA-ALL by performing RNA-seq analysis of Philadelphia chromosome (Ph)-negative AYA-ALL specimens (n = 73) with the use of a next-generation sequencer. Interestingly, insertion of D4Z4 repeats containing the DUX4 gene into the IGH locus was frequently identified in B cell AYA-ALL, leading to a high level of expression of DUX4 protein with an aberrant C terminus. A transplantation assay in mice demonstrated that expression of DUX4-IGH in pro-B cells was capable of generating B cell leukemia in vivo. DUX4 fusions were preferentially detected in the AYA generation. Our data thus show that DUX4 can become an oncogenic driver as a result of somatic chromosomal rearrangements and that AYA-ALL may be a clinical entity distinct from ALL at other ages.

Numerous variants of unknown significance (VUS) have been identified through large-scale cancer genome projects, although their functional relevance remains uninvestigated. We developed a mixed-all-nominated-mutants-in-one (MANO) method to evaluate the transforming potential and drug sensitivity of oncogene VUS in a high-throughput manner and applied this method to 101 nonsynonymous epidermal growth factor receptor (EGFR) mutants. We discovered a number of mutations conferring resistance to EGFR tyrosine kinase inhibitors (TKIs), including gefitinib- and erlotinib-insensitive missense mutations within exon 19 and other gefitinib-resistant mutations, such as L833V, A839T, V851I, A871T, and G873E. -positive tumors (12.8%) harbored compound mutations primarily in the allele, which decreased the gefitinib sensitivity of these tumors. The MANO method further revealed that some EGFR mutants that are highly resistant to all types of TKIs are sensitive to cetuximab. Thus, these data support the importance of examining the clinical relevance of uncommon mutations within and of evaluating the functions of such mutations in combination. This method may become a foundation for the in vitro and in vivo assessment of variants of cancer-related genes and help customize cancer therapy for individual patients.

Rhabdomyosarcoma (RMS), a cancer of skeletal muscle lineage, is the most common soft-tissue sarcoma in children [1]. Major subtypes of RMS include alveolar (ARMS) and embryonal (ERMS).[2, 3] Whereas ARMS typically contain translocations generating the PAX3-FOXO1 or PAX7-FOXO1 aberrant transcription factors which block terminal myogenic differentiation [4-6], no functionally comparable genetic event has been found in ERMS. Here, we report the discovery, through whole exome sequencing, of a recurrent somatic point mutation Leu122Arg in the myogenic transcription factor, MYOD1, in a distinctive subset of ERMS with poor outcomes that also often contain PI3K/AKT pathway mutations. Previous mutagenesis studies had shown that MYOD1 Leu122Arg can block wild-type MYOD1 function and bind to MYC consensus sequences [7], suggesting a possible switch from differentiation to proliferation. Our functional data now confirm this prediction. RMS with MYOD1 Leu122Arg represents a molecularly defined subset of RMS eligible for high risk protocols and targeted therapeutic development.

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