This week's artwork was donated by Gavin, a pediatric cancer patient who received treatment at The Children's Hospital of Philadelphia .
Strong evidence exists tying estrogen exposure to breast cancer .
For example, women who have early menopause, late menarche and low parity are at increased risk for breast cancer . In fact, some researches believe that endogenous sex hormones are the key to understanding the etiology of breast cancer. Physical activity may alter the metabolism of estrogen and therefore may influence a women's risk of breast cancer. Several studies have examined the association of exercise and breast cancer risk but no firm conclusions can be drawn from these studies most of which are small and with limited follow up. A recent study reported in the New England Journal of medicine overcomes these shortcomings and helps establish a more definitive link between the risk of breast cancer and physical activity.