A number of studies suggest that current use of oral contraceptives (birth control pills) appears to slightly increase the risk of breast cancer, especially among younger women. However, the risk level goes back to normal 10 years or more after discontinuing oral contraceptive use.

http://www.cancer.gov/cancertopics/factsheet/Risk/oral-contraceptives

Well, studies also show that use of oral contraceptives for longer than a year decreases the chance of getting uterus cancer...