Editorial

Cancer, currently the second cause of death worldwide, is a major public health problem that soon may overtake heart disease as the leading cause of death [1]. Breast cancer is not a single disease but a diverse set of diseases characterized by heterogeneity in histology, genomic aberrations, and protein expression that influence treatment response and patient outcome [2].

The processes underlying cancer development are still not fully understood, but most of the theories are based on a model composed of two basic events, i.e. a change in the genetic material of cells, and altered cell division and transmission of their genetic material to daughter cells [3].

Numerous factors have been proposed as possible agents involved in the initiation and/or development of tumors. This information stems from a multitude of epidemiological studies, in which a number of common features in the history of subjects with cancer were observed. Among the important contributing factors are diet, smoking, contact with toxic substances, alcohol consumption, infection by different pathogens, various types of radiation and environmental pollution [4].

Throughout the years, researchers have sought to verify other lifestyle aspects that could contribute to reducing the development of cancer. As such, one of the promising tools against cancer is physical activity [5].

Individuals who regularly do physical activity experience numerous health benefits, including reduced incidence of heart and metabolic diseases and increased longevity [6,7]. Thus, the question arises as to whether there is also an association between physical activity and lower cancer incidence; this hypothesis of the cancer-reducing effect of exercise is not new: already in 1922, Cherry found that men with physically active jobs had lower cancer mortality/ incidence rates than men involved in less active jobs. Inactivity levels are disconcerting given substantial epidemiologic evidence showing that physical activity is associated with decreased risks of breast cancers. For example, insufficient physical activity levels are associated with cause 9% of breast cancer cases and 10% of colon cancer cases in Europe. The biologic pathways underlying the association between physical activity and cancer risk are incompletely defined, but potential etiologic pathways include insulin resistance, growth factors, adipocytokines, steroid hormones, and immune function [6,8].

Physical activity might have a positive influence on the immune system. Therefore, multiple studies have explored the role of the immune response in tumorigenesis, which is now known to be either stimulatory or inhibitory. The intercellular interactions and cytokine pathways polarize the tumor microenvironment, resulting in either tumor-promoting or tumor-inhibiting effects.

The tumor microenvironment includes, next to the extracellular matrix and stroma cells, innate immune cells (macrophages, neutrophils, myeloid-derived suppressor cells, natural killer cells, and dendritic cells) and adaptive immune cells (B and T lymphocytes) [9]. It is noteworthy, however, that many specific aspects of the mechanisms that contribute to cancer have unknown properties [10]. In addition, the physical activity-related pathways of the immune system, aimed at preventing and even fighting cancer, have not been fully elucidated, although it already has in the literature studies evidencing a polarization of the antitumor patterns of the immunological response to physical activity [11-14].

References

1. Siegel RL, Miller KD, Jemal A (2015) Cancer Statistics, 2015. CA Cancer J Clin 65: 5-29.
2. Whittle JR, Lewis MT, Lindeman GJ, Visvader JE (2015) Patient-derived xenograft models of breast cancer and their predictive power. Breast Cancer Research 17:17.
3. Cooper GM. The Cell: Molecular Approach. 2nd Ed. Sinauer Associates, Sunderland, Massachusetts, US; 2000.
4. Anand P, Kunnumakara AB, Sundaram C, Harikumar KB, Tharakan ST, et al. (2008) Cancer is a Preventable Disease that Requires Major Lifestyle Changes. Pharmaceutical Research 25(9): 2097-2116.
5. Marchand LL, Kolonel LN, Yoshizawa CN (1991) Lifetime occupational physical activity and prostate cancer risk. American Journal of Epidemiology 133: 103-111.
6. Harvie M, Howell A, Evans DG (2015) Can Diet and Lifestyle Prevent Breast Cancer: What Is the Evidence? Am Soc Clin Oncol Educ Book 35: e66-73.
7. Senany SA, Saif AA (2015) Assessment of physical health status and quality of life among Saudi older adults. J Phys Ther Sci 27(6): 1691-1695.
8. Leitzmann M, Powers H, Anderson AS, Scoccianti C, Berrino F, et al. (2015) European Code against Cancer 4th edition: Physical activity and cancer. Cancer Epidemiol Suppl 1: S46-55.
9. Mantovani A, Romero P, Palucka AK, Marincola FM (2008) Tumour immunity: effector response to tumour and role of the microenvironment. The Lancet 371(9614): 771-783.
10. Trichopoulos D, Li FP, Hunter DJ (1996) What causes cancer? Scientific American 50-57.
11. Abdalla DR, Murta EFC, Michelin MA (2013) The influence of physical activity on the profile of immune response cells and cytokine synthesis in mice with experimental breast tumors induced by 7,12-dimethylbenzanthracene. Eur J Cancer Prev 22: 251-258.
12. Abdalla DR, Aleixo AAR, Murta EFC, Michelin MA (2014) Innate immune response adaptation in mice subjected to administration of DMBA and physical activity. Oncol Lett 7(3): 886-890.
13. Abdalla DR, Gomes BBM, Murta EFC, Michelin MA (2017) Bone marrow-derived dendritic cells under influence of experimental breast cancer and physical activity. Oncol Lett 13(3): 1406-1410.
14. Bianco TM, Abdalla DR, Desidério CS, Thys S, Simoens C, et al. (2017) The influence of physical activity in the anti-tumor immune response in experimental breast tumor. Immunol Lett 190: 148-158.