Location matters: Spatial-dependent effects of myofibroblasts modulate survival in breast cancer.

While cancer-associated fibroblasts (CAFs) have been historically considered pro-tumorigenic, several studies found that myofibroblast-like CAFs (myCAFs) may have tumor-restraining properties. Here, we show that myofibroblasts exhibit location-dependent effects in breast cancer progression. Deconvolution of bulk RNA sequencing data from The Cancer Genome Atlas showed that high intratumoral myCAF abundance in ER+/PR+/HER2- breast tumors is associated with poor patient overall survival, whereas an inverse association was observed for peritumoral myCAFs in tumor-adjacent normal tissues. Single-nucleus RNA sequencing of 2 ER+/PR+/HER2- invasive breast carcinomas and their matched peritumoral tissues identified high abundance of myCAFs in the larger tumor, whereas a distinct myofibroblast-like sub-population was found in the peritumoral tissues of the smaller tumor. Three-dimensional co-culture experiments demonstrated that myofibroblasts positioned outside the tumor spheroid reduced breast cancer cell invasion. These data highlight that the spatial location of myofibroblasts determines their effects and provides an explanation for their dual role in cancer biology.