P2RX7 and breast cancer: In order to decipher the role of P2X7R expressed by the cells of an organism hosting a mammary tumour, most importantly the immune cells, on primary tumour growth and metastasis development, we implanted CTL cells with two cell density (1 × 106 or 1 × 104 cells) in the fifth mammary fat-pad of either wild-type (P2rx7+/+) or knock-out (P2rx7−/−) BALB/cJ mice (Figure 4e).