Organ-specific tropism and adaptation after metastasis of ER+ breast cancers

Patients diagnosed with estrogen receptor (ER) positive breast cancer have a prolonged risk of distal metastatic recurrence to vital organs. Metastatic disease is incurable at present due to the development of treatment resistant cell populations. Here we used single-cell RNA sequencing to evaluate the transcriptome heterogeneity of ER+ breast cancer patient-derived xenografts (PDX) tropic for three common breast cancer metastatic sites – bone, brain, and liver – compared to primary tumors grown in the mammary fat pad. Metastatic cell populations at each location were phenotypically distinct from primary tumor cells with unique transcriptional programs indicative of signaling programs driven by specific transcription factors. Cells that metastasized to brain and liver tissue adopted gene expression programs indicative of the target organ microenvironments. Discerning the organ-specific phenotypic adaptations of metastatic ER+ breast cancer cells may help tailor appropriate therapies for individual patients and to each metastatic site. Overall design: Single-cell RNA-seq analysis of human breast cancer patient derived xenografts in mice.