SignificanceDespite concerted efforts to identify causal genes that drive breast cancer (BC) initiation and progression, we have yet to establish robust signatures to stratify patient risk. Here we used in vivo transposon-based forward genetic screening to identify potentially relevant BC driver genes. Integrating this approach with survival prediction analysis, we identified six gene pairs that could prognose human BC subtypes into high-, intermediate-, and low-risk groups with high confidence and reproducibility. Furthermore, we identified susceptibility gene sets for basal and claudin-low subtypes (21 and 16 genes, respectively) that stratify patients into three relative risk subgroups. These signatures offer valuable prognostic insight into the genetic basis of BC and allow further exploration of the interconnectedness of BC driver genes during disease progression.

30The systematic identification of genetic events driving cellular transformation and tumor progression in the absence 31 of a highly recurrent oncogenic driver mutation is a challenge in cutaneous oncology. In cutaneous squamous cell 32 carcinoma (cuSCC), the high UV-induced mutational burden poses a hurdle to achieve a complete molecular 33 landscape of this disease. Here, we utilized the Sleeping Beauty transposon mutagenesis system to statistically 34 define drivers of keratinocyte transformation and cuSCC progression in vivo in the absence of UV-IR, and identified 35 established tumor suppressor genes, as well as previously unknown oncogenic drivers of cuSCC. Functional analysis 36 confirms an oncogenic role for the ZMIZ genes, and tumor suppressive roles for KMT2C, CREBBP and NCOA2, in the 37 initiation or progression of human cuSCC. Taken together, our in vivo screen demonstrates an extremely 38 heterogeneous genetic landscape of cuSCC initiation and progression, which could be harnessed to better 39 understand skin oncogenic etiology and prioritize therapeutic candidates. 40

The identification of lower-performance amplicons will be informative to laboratories intending to use this panel. We have also demonstrated proof-of-concept that different libraries (TruSight Myeloid and Nextera XT) can be combined and sequenced on the same flow cell to generate additional reads for CEBPA.