Metastasis of triple negative breast cancer is regulated by a targetable miR-342-E2F network.

Triple-negative breast cancer (TNBC) has a high incidence of metastasis and limited therapeutic options. Here, we identify a multimodal and targetable miR-342-E2F network that regulates metastatic outgrowth in TNBC. Through integrating clinical and experimental datasets, we uncover miR-342 as a suppressor of TNBC metastasis. Temporal re-expression of miR-342 significantly inhibited metastatic progression in both immunocompetent and xenograft TNBC models by specifically limiting the outgrowth of disseminated tumour cells. Using multi-omics profiling, we identified the global complement of miR-342 targets, demonstrating that it directly suppresses transcriptional and post-transcriptional networks that converge to dampen E2F signalling. Single-cell analysis of matched primary and metastatic patient-derived TNBC samples reveals activation of E2F signalling in metastasis that corresponds with reduced miR-342 host gene EVL expression. Furthermore, pharmacologic inhibition of this pathway with the CDK4/6 inhibitor palbociclib specifically reduces metastatic outgrowth of pre-established TNBC lesions. Our findings reveal that TNBCs with low miR-342/high E2F signalling have increased metastatic competency and may be amenable to CDK4/6 inhibitor therapy, offering a potential strategy for targeted intervention to limit TNBC metastasis.