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

Duclos Martine

*1Department of Sport Medicine and Functional Explorations, University-Hospital (CHU), Hopital G. Montpied, Clermont-Ferrand 2 INRA, UMR 1019, Clermont-Ferrand 3University Clermont 1, UFR Médecine, Clermont-Ferrand 4CRNH-Auvergne, Clermont-Ferrand France* 

### **1. Introduction**

108 Topics in Cancer Survivorship

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> 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

Physical Activity and Cancer: It is Never Too Late to Get Moving! 111

directly prevent lower colon cancer. The association has been consistently reported in many studies of various designs, in diverse populations, for men and women, and after statistical control for a variety of other lifestyle factors. A compelling finding is that the inverse association has been observed for both leisure-time and occupational activities, for which

The characteristics of physical activity which could have a protective effect towards colon cancer remained controversial, the data of the literature being contradictory. The categorizations and the methods of measure of physical activity which differ between studies are probably at the origin of these inconsistencies. Measuring physical activity in all its components, type, intensity and duration is complex. Although the results are heterogeneous, the available evidence suggest that at least 30-60 minutes per day of moderate to vigorous intensity for at least 5 days per week is required to significantly

Concerning the optimal period of life to practice physical activity to maximize its protective effect, the authors recommend a regular practice of physical activity throughout the life.

More than a dozen of cohort studies and an even more important number of case-control studies have examined the relations between physical activity and risk of breast cancer. More than three quarters of these studies have observed a beneficial of physical activity on breast cancer risk with a risk reduction about 25% when comparing the most to least active subjects. These results were confirmed and specified in a review of articles published between 1994 and 2006 on the relations between risks of breast cancer and physical activity (Monninkhof et al., 2007). The methodological quality of these articles was calculated on the basis of a statistical quality score and only articles of high quality were eligible: 19 cohort studies and 29 case-control studies. The higher quality cohort studies showed a risk reduction ranging from 20 to 40%. A more recent overview of the existing evidence relating physical activity to breast cancer risk has been recently published (73 studies) (Friedenreich et al., 2010). They found a consistent reduction of about 25% of breast cancer risk when comparing the most to least active study participants (Friedenreich et al., 2010). Moreover, there is consistent evidence of a dose-response effect of decreasing risk with increasing

**2.2.2 What type of physical activity is associated with prevention of breast cancer ?**  Most studies have investigated the association between breast cancer and leisure physical activity (walking, cycling, swimming, gymnastics) but few studies have included low intensity leisure physical activity such as gardening, home repair, stair climbing or housework (cleaning, washing, cooking, child care…) which probably led to an underestimation of total energy expenditure, especially among women who do not have access to a sport activity. The inclusion in the physical activity questionnaires of household activity is important because it is one of the main sources of physical activity for women in most developed countries. This is highlighted in the European cohort EPIC (The European Prospective Investigation into Cancer and Nutrition study), which showed that the risk of breast cancer was reduced in women in the top quartile of household activities (>90 METh/wk) compared with women in the lowest quartile activities (<28 MET-h/wk): -19% for

**2.2.1 Review of the evidence on physical activity and breast cancer prevention** 

patterns of potential confounding lifestyle characteristics are likely to differ.

reduce the risk of colon cancer (Friedenreich et al., 2010).

**2.2 Breast cancer**

activity levels.

on the current guidelines on physical activity for cancer prevention and for cancer survivors, with guidance based largely on proven associations that exist between physical activity and specific comorbid conditions (such as heart disease or osteoporosis) to which cancer survivors are especially prone, or associations between physical activity and other factors, such as quality of life, functional decline, and fatigue. Effective strategies to increase physical activity will be discussed.
