Today, although science and technology have greatly developed, cancer is still under the shadow of prejudice and considered as a death sentence. As for who is to blame for this situation, we should not forget the actual influence of natural, technical and social environment in which we all live and offer or receive various forms of energy. Various kinds of radiation including radiation from the sun are found in our natural environment and radiation from the sun contributes especially to the development of melanoma. In our social environment we tend to develop harmful habits such as smoking and alcohol drinking, to have insufficient physical exercise and increased body weight. All these habits are concidered potentially carcinogenic. A new branch of medicine, which also tries to diagnose and treat cancer has been created lately. This is the speciality of Nuclear Medicine which has developed since 1945. This new specialty, aided by modern equipment has many useful diagnostic and therapeutic applications against cancer as mentioned in this lecture.