PHLDA2 promotes breast cancer metastasis by co-opting a developmental program for placental vascular remodeling.

Identifying drivers of metastasis is essential for developing new treatments for patients with advanced disease. Here, we identify PHLDA2 as a robust driver of breast cancer metastasis. Previous work established PHLDA2 as an imprinted gene expressed by trophoblasts which are critical for vascular remodeling during placental development. We find that hypomethylation of PHLDA2 in breast tumors correlates with increased gene expression, which is associated with metastasis and poor survival in breast cancer patients. RNA-sequencing showed that PHLDA2 overexpression results in upregulation of genes that control invasion, extracellular matrix assembly, and vascular remodeling, consistent with trophoblast functions in placental development. Using an in vitro vascularized microtumor (VMT) system, we find that PHLDA2 functions through SPARC, which promotes metastasis by inducing vascular permeability and enhancing tumor dissemination. These data suggest that increased expression of PHLDA2 through hypomethylation promotes metastasis by ectopic expression of a developmental program for vascular remodeling.