In recent years medical ethics has become an undisputed part of medical studies. Many people believe that modern advances in medical technology - such as the development of dialysis machines, respirators, magnetic resonance imaging and genetic testing and types of cancer screenings - have created bioethical dilemmas that confront physicians in the 21st century. Debates over research and screening ethics have until recently revolved around two related questions: the voluntary, informed consent of subjects, and the appropriate relationship between risk and benefit to subjects. Every patient has a right to full and accurate information about his or her medical condition. This legal principle arose primarily through court decisions concerning informed consent, but over time physicians recognized that most patients prefer to learn the truth about their condition and use the information well. To screen is to search for disease in the absence of symptoms or, in other words, to attempt to find disease in someone not thought to have a disease. Examples of screening include routine mammography to detect breast cancer, routine pap smears to detect cervical cancer, and routine Prostate Specific Antigen (PSA) testing to detect prostate cancer. Ethical principles to be followed in cancer screening programmes are intended mainly to minimize unnecessary harm for the participating individuals. Numerous ethical questions can be raised about the practice of screening for disease. Here, we examine four leading cancer killers worldwide and we review the screening of protocols of these cancer types and their possible ethics.