​Discuss how physical activity (PA) can protect people against the risks of various cancers.

​Among hundreds of research studies on the relationship between PA and cancers, several reviews focused on evaluating mostly studies on colorectal, breast, endometrial, prostate, and lung cancer. PA protects against all these cancers.
The strongest evidence of this is for colorectal and breast cancer.
PA's protection against colorectal cancer appears equally strong for both women and men.
PA seems to protect postmenopausal women against breast cancer more than premenopausal women, and non-Caucasian women more than Caucasian women.
Moderate to high PA levels appear to reduce lung cancer incidence in both sexes, but more for women than men.
While it is not clearly known how PA lowers cancer risk, research suggests two possible reasons:
PA may influence the initiation and growth of tumors.
PA influences proinflammatory cytokines, which are involved in cancer (as well as cardiovascular disease) development.
People who already have cancer may also benefit from exercising.
PA benefits chemotherapy patients by increasing their aerobic fitness, weight, and strength.
PA also helps patients manage the fatigue that cancer treatment often causes.
Hence PA is effective for both preventing several kinds of cancers and managing treatment side-effects.