Abstract
Natural killer (NK) cells from the innate immune system are integral to overall immunity and also in managing the tumor burden during cancer. Breast (BCa) and prostate cancer (PCa) are the most common tumors in U.S. adults. Both BCa and PCa are frequently treated with hormone suppression therapies that are associated with numerous adverse effects including direct effects on the immune system. Regular exercise is recommended for cancer survivors to reduce side effects and improve quality of life. Acute exercise is a potent stimulus for NK cells in healthy individuals with current evidence indicating that NK mobilization in individuals with BCa and PCa is comparable. NK cell mobilization results from elevations in shear stress and catecholamine levels. Despite a normal NK cell response to exercise, increases in epinephrine are attenuated in BCa and PCa. The significance of this potential discrepancy still needs to be determined. However, alterations in adrenal hormone signaling are hypothesized to be due to chronic stress during cancer treatment. Additional compensatory factors induced by exercise are reviewed along with recommendations on standardized approaches to be used in exercise immunology studies involving oncology populations.
Highlights
Several outcomes contain only limited evidence supporting the potential benefits of exercise such as chemotherapy-induced neuropathy, cardiotoxicity, falls and cognitive function while others that have direct effects on the tumor control and management are not included at this stage due to insufficient evidence
In laboratory-controlled settings in BCa and prostate cancer (PCa), Natural killer (NK) cell mobilization is relatively consistent with studies demonstrating robust increases in the absolute number and cell frequency immediately following exercise
BCa and the controls demonstrated consistent responses in terms of NK cells and other lymphocyte subpopulations. This suggests that a longer duration or more intense acute exercise does not increase the risk to cancer survivors with normal immune cell frequency distribution
Summary
The primary role of the immune system is to manage infections by reducing the initial pathogen growth and the development of long-term immunity to reduce the risk or length of future exposures. As in many physiological systems, the immune function is age-dependent as the susceptibility to disease and infection increases in older individuals [2]. This higher degree of immunosenescence likely contributes to several of the common causes of death in older populations including cancers, sepsis, influenza/pneumonia and nephritis [3]. NK cell counts immediately post-exercise with cellular egress causing circulating levels to drop (even below baseline) as cells migrate into the tissue before returning to resting levels [10,11,12] This biphasic response (see Figure 1) is affected by the exercise dose with higher intensity [13,14] and aerobic exercise [15] producing a greater NK mobilization. NK cell type impacts the response with CD56bright being less responsive to exercise than the more cytotoxic CD56dim population [5]
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