H istory teaches that the discovery of cure for a disease rarely precedes the knowledge of its cause. Therefore, it is perhaps important to review attempts, in a timeline presentation, that were made to discover the cause of cancer in humans.
Ancient peoples from prehistoric times believed that cancer was caused by evil spirits, natural forces, contact with wicked men, and disharmony of the planets. According to Hebrew, Greek, and Roman teachings, cancer was caused by sin, violation of religious rules, and the wrath of gods. Hippocrates (BC 460-375) and his disciples were opposed to superstitions and hypothesized that excess or deficiency of blood, mucus, and bile could cause cancer, particularly in old age. Galen (AD 131-203) and his followers, in the Roman Empire and beyond, believed that accumulation of black bile in the breast, uterus, lips, and hemorrhoids caused cancer. Galen's theory was accepted as doctrine by medical practitioners and organized religions for sixteen centuries with little modification. In the early Middle Ages, accumulation of noxious substances in blood as cause of disease, including cancer, was added to Galen's humoral theory and led to introduction of blood letting. Although alchemists, astrologers, and contagion theorists pressed their own thoughts, Galen's doctrine withstood all challenges throughout the Middle Ages. 1 With revolutionary fervor, an outspoken Swiss physician and chemist, Paracelsus (1493-1541), was the first to openly oppose the Galenists, and Paracelsus almost got away with it. But his opponents caught up with him in Salzburg, Austria, and beat him to death. Paracelsus proposed that deposits of salt of sulfur and arsenic in blood cause cancer, particularly in miners, masons, chemists, and metallurgists. 2 He left for us the first description of an association between occupational diseases and cancer. Ambroise Pare Β΄(1510-1590), a distinguished French surgeon, felt that the antecedent cause of cancer was an irregular diet that induced accumulation of feculent material in the blood. Overheating changed this material to a corrosive substance that produced ulceration of the cancer. 3 Discoveries by anatomists in the 1500s, discovery of blood circulation in 1628 by William Harvey (1578-1657), and the description of lymphatics by Thomas Bartholin (1616-1680) in 1656 introduced the concept of coagulation and fermentation of the blood and lymph as the cause of cancer. By observing deterioration (ulceration and necrosis) of various organs harboring cancer, surgeons pointed out that cancer was a destructive growth and was caused by internal structural transformation of glandular and vascular organs. 4 Although surgeons