Physical Activity and Cancer: It is Never Too Late to Get Moving!

In terms of prevalence, the most common cancers in men and women worldwide are breast cancer (3.9 million breast cancer cases) and colorectal cancers (2.4 million). Moreover, the worldwide incidence of breast and colorectal cancers is destined to increase substantially in the next few decades. Therefore, the prevention of the occurrence of these various types of cancers represents a real stake in public health for which physical activity could play an important role. Indeed, numerous studies showing an association between prevention of these cancers and physical activity have been published these last years. The number of survivors after treatment of a cancer ("cancer survivors") is also increasing. Since last years, different studies have rocked the research community involved in cancer survivorship. These studies reported a significant protective association between increased physical activity that occurred after the diagnosis of breast or colon cancer and recurrence, cancer-related mortality, and overall mortality among breast cancer or colon cancer survivors. This chapter will consider epidemiologic evidence regarding the association between physical activity and breast and colon cancer in primary prevention (cancer occurrence) and in tertiary prevention (cancer recurrence). The second aim of this chapter will be to discuss the type and characteristics (duration, intensity) of physical activity associated with these effects both in primary prevention of breast and colon cancer and in cancer survivors. In other words, what types of exercise are most beneficial? Evidence for the underlying mechanistic targets of physical activity interventions on the carcinogenesis process is also emerging. Studies suggest that exercise can exert its cancerpreventive effects at many stages during the process of carcinogenesis, including both tumour initiation and progression. This will be discussed in the third part of this chapter. In the fourth part, the barriers to prescribe physical activity in physicians will be discussed as the published work provides sufficient evidence to suggest that physical activity is safe and well-tolerated even in cancer survivors and that oncologists can recommend to their patients physical activity after the completion of primary treatment. Finally we will discuss