Does regular aerobic exercise lower an individual's risk of developing cancer?

Likely yes. This likely lowers a person's risk for cancer since it helps the cardiovascular system and keeps a person active. This likely helps the body to be purged of residual waste and toxins that might indirectly lead to cancer, and keeps one from leadxing a sedentary lifestyle. Such a life could lead to over-indulgance of food, alcohol, cigerrettes, which could clearly predispose to many a cancer.
Yes. Exercise, through control of obesity and additional mechanisms that are not fully defined, reduces the risk of cancer. It is even more important in reducing mortality from cardiovascular disease.