Exercise
“Those who think they have not time for bodily exercise will sooner or later have to find time for illness.” Edward Stanleys (1799 – 1869)
There is solid epidemiological evidence that regular exercise offers protection against cancer development and recurrence, even when started late in life.  Regular exercise induces anti-inflammatory actions, stimulates the immune system, and helps developing a healthier psychological profile. Several studies have confirmed such theories. For example in a study conducted by Harvard Medical School, women who walked 3 to 5 hours per week had a 50% reduction in the risk of breast cancer recurrence - some of the best drugs we have do not do better than that.
 
 
 
Warning!
You should contact your physician before undertaking any physical exercise.
References
 
Harvard Health Publications, August 2005, “Exercise helps breast cancer survivors live longer”, https://www.health.harvard.edu/newsweek/Exercise_helps_breast_cancer_survivors_live_longer.htm, Retrived 27 March 2009
Holick CN, Newcomb PA, Trentham-Dietz A, Titus-Ernstoff L, Bersch AJ, Stampfer MJ, Baron JA, Egan KM, Willett WC, “Physical activity and survival after diagnosis of invasive breast cancer”, Cancer Epidemiol Biomarkers Prev. 2008 Feb;17(2):379-86
Holmes MD, Chen WY, Feskanich D, Kroenke CH, Colditz GA, “Physical activity and survival after breast cancer diagnosis”, JAMA. 2005 May 25;293(20):2479-86
Irwin ML, Smith AW, McTiernan A, Ballard-Barbash R, Cronin K, Gilliland FD, Baumgartner RN, Baumgartner KB, Bernstein , “Influence of pre- and postdiagnosis physical activity on mortality in breast cancer survivors: the health, eating, activity, and lifestyle study”, J Clin Oncol. 2008 Aug 20;26(24):3958-64
Mathur N, Pedersen BK, “Exercise as a mean to control low-grade systemic inflammation”, Mediators Inflamm. 2008;2008:109502
Meyerhardt JA, Giovannucci EL, Holmes MD, Chan AT, Chan JA, Colditz GA, Fuchs CS, “Physical activity and survival after colorectal cancer diagnosis”, J Clin Oncol. 2006 Aug 1;24(22):3527-34
O. Carl Simonton M.D., Stephanie Mathews-Simonton, James L. Creighton, ìGetting Well Againî, Bantam 1980
Peel JB, Sui X, Adams SA, Hébert JR, Hardin JW, Blair SN, “A prospective study of cardiorespiratory fitness and breast cancer mortality”, Med Sci Sports Exerc. 2009 Apr;41(4):742-8
Peel JB, Sui X, Matthews CE, Adams SA, Hébert JR, Hardin JW, Church TS, Blair SN, “Cardiorespiratory Fitness and Digestive Cancer Mortality: Findings from the Aerobics Center Longitudinal Study”, Cancer Epidemiol Biomarkers Prev. 2009 Mar 17
Speed-Andrews AE, Courneya KS, “Effects of exercise on quality of life and prognosis in cancer survivors”, Curr Sports Med Rep. 2009 Jul-Aug;8(4):176-81