SPI1 and breast cancer: Each population appears to be unable to fully compensate the other upon depletion: we report that targeted ablation of BC cells results in a significant decrease in NG2-positive MCs at E15.5 and, conversely, Yamazaki and colleagues have shown that in PU.1 (also known as Spi1) mutants, depleted of tissue myeloid cells, there is also a loss of MCs at E15.5 (Yamazaki et al., 2017).