A marked reduction in numbers of proliferative and mitotic cells was observed in PyMT-Fib-cKO mammary tumours at the early- and advanced stages, whereas numbers of pro-apoptotic cells were comparable in PyMT-Fib-WT and PyMT-Fib-cKO mammary tumours at both stages (Fig. 4a, b; Supplementary Fig. 4a, b). The gene discussed is FBL; the disease is breast cancer.