Spontaneous physical activity decreases spleen weight in correlation with tumour volume. (A) Correlation between tumour volume and spleen weight independent of environment, data were analysed by Pearson’s correlation test (n = 10 mice/group) (B) Spleen weight depending on the environment, results are grams (n = 10 mice/group) (C) Spleen CD4+ CD8+ maturation, results are in cells per mg of tissue. (D) Spleen CD4+ CD8− maturation, results are in cells per mg of tissue. (E) Spleen CD4− CD8+ maturation, results are in cells per mg of tissue. Phenotyping is performed on 5 mice spleen/group. Data are mean ± SEM. Data were analysed by Mann–Whitney t-test. Representative data are shown: * p ˂ 0.05, SE vs. EE.