1970s

• Studies in human populations link cancer risk to infectious agents, such as human papillomavirus (cervical cancer) and hepatitis B (liver cancer).

• Statistical methods developed to control simultaneously for several factors in the analysis of studies and to quantify cancer risks.

• Studies clarify the patterns of cancer risk following exposure to ionizing radiation.

• Studies link cancer risks to hormonal drugs, such as diethylstilbestrol (DES) taken during pregnancy and hormonal replacement therapy.

• Flexible sigmoidoscopy and colonoscopy developed to help find and remove precancerous growths.