(A) Wild type (WT) and MMTV-PyMT (PyMT) mice on the FVB background were allowed to exercise voluntarily (in running wheels, runners) or left non-exercised (locked running wheels, non-runners) between 4 and 12 weeks of age. (B) Running distance (km/day) in WT and PyMT mice. *p<0.05, two-tailed unpaired t test. (C) Tumor volume measured twice weekly for PyMT running and non-running mice. Mean and SEM (n = 10–11). (D) Survival of PyMT mice, runners, and non-runners. Survival curve ns = not significant, Log-rank (Mantel-Cox) test, (n = 10–11). (E) Tumor initiation as age (day) of first indication of a palpable tumor in running (Runners) and non-running (Non-runners) PyMT mice. n = 11, ns = not significant, two-tailed t test. (F) Tumor stage from histological scoring (1-4) in mammary glands of running and non-running PyMT mice at 12 (n = 6–10) and 8 (n = 4) weeks of age, ns = not significant, two-tailed t test. (G) Individual body weight for WT and PyMT running and non-running mice. n = 7–10, ns = not significant, one-way ANOVA with Tukey’s multiple comparison test. (H) Immunohistological characterization of PyMT tumors from non-running and running mice using CD3, F4/80, PCNA, Podocalyxin (PODXL), and Granzyme B (GZMB) antibodies, respectively. n = 8–15, ns = not significant, *p<0.05, Two-tailed unpaired t test. (I) Flow-cytometry-based frequency of macrophages within I3TC tumor. Ns = not significant, two-tailed t-test. (J) Flow-cytometry-based frequency of neutrofiles within I3TC tumor. Ns = not significant, two-tailed t-test.