Identification of clinically relevant drivers of breast cancers in intact mammary epithelium is critical for understanding tumorigenesis yet has proven challenging. Here, we show that intra-amniotic lentiviral injection can efficiently transduce progenitor cells of the adult mammary gland and use that as a platform to functionally screen over 500 genetic lesions for functional roles in tumor formation. Targeted progenitors establish long-term clones of both luminal and myoepithelial lineages in adult animals, and via lineage tracing with stable barcodes, we found that each mouse mammary gland is generated from a defined number of ∼120 early progenitor cells that expand uniformly with equal growth potential. We then designed an in vivo screen to test genetic interactions in breast cancer and identified candidates that drove not only tumor formation but also molecular subtypes. Thus, this methodology enables rapid and high-throughput cancer driver discovery in mammary epithelium.

在完整的乳腺上皮中确定乳腺癌的临床相关驱动因素对于理解肿瘤发生至关重要，但已证明具有挑战性。在这里，我们显示羊膜内慢病毒注射可以有效地转导成年乳腺的祖细胞，并以此为平台来功能筛选500多个遗传性病变在肿瘤形成中的功能。靶向祖细胞在成年动物中建立管腔和肌上皮细胞系的长期克隆，并且通过使用稳定条形码的谱系追踪，我们发现每只小鼠的乳腺都是由一定数量的〜120个早期祖细胞产生的，这些祖细胞均等地生长且均等生长潜在。然后我们设计了一个体内筛查乳腺癌中的遗传相互作用，并鉴定出不仅推动肿瘤形成而且推动分子亚型的候选药物。因此，该方法使得能够在乳腺上皮中快速且高通量地发现癌症驱动器。