From the earliest times, physicians have puzzled over the causes of cancer. Ancient Egyptians blamed cancers on the gods.
Hippocrates believed that the body had 4 humors (body fluids) :blood, phlegm, yellow bile, and black bile. When the humors were balanced, a person was healthy. Too much or too little of any of the humors caused disease. An excess of black bile in various body sites was thought to cause cancer. This theory of cancer was passed on by the Romans and was embraced by the influential doctor Galen’s medical teaching, which remained the unchallenged standard through the Middle Ages for over 1,300 years. During this period, the study of the body, including autopsies, was prohibited for religious reasons, which limited progress of medical knowledge.
Among theories that replaced the humoral theory of cancer, was the formation of cancer by another body fluid, lymph. Life was believed to consist of continuous and appropriate movement of the fluid parts of the body through the solid parts. Of all the fluids, the most important were blood and lymph. Stahl and Hoffman theorized that cancer was composed of fermenting and degenerating lymph varying in density, acidity, and alkalinity. The lymph theory gained rapid support. The eminent Scottish surgeon John Hunter (1728−1793) agreed that tumors grow from lymph constantly thrown out by the blood.
In 1838, German pathologist Johannes Muller demonstrated that cancer is made up of cells and not lymph, but he believed that cancer cells did not come from normal cells. Muller proposed that cancer cells developed from budding elements (blastema) between normal tissues. His student, Rudolph Virchow (1821−1902), the famous German pathologist, determined that all cells, including cancer cells, are derived from other cells.
Chronic irritation theory
Virchow proposed that chronic irritation was the cause of cancer, but he falsely believed that cancers “spread like a liquid.” In the 1860s, German surgeon, Karl Thiersch, showed that cancers metastasize through the spread of malignant cells and not through some unidentified fluid.
Despite advances in the understanding of cancer, from the late 1800s until the 1920s, trauma was thought by some to cause cancer. This belief was maintained despite the failure of injury to cause cancer in experimental animals.
Infectious disease theory
Zacutus Lusitani (1575−1642) and Nicholas Tulp (1593−1674), 2 doctors in Holland, concluded at almost the same time that cancer was contagious. They made this conclusion based on their experiences with breast cancer in members of the same household. Lusitani and Tulp publicized the contagion theory in 1649 and 1652, respectively. They proposed that cancer patients should be isolated, preferably outside of cities and towns, in order to prevent the spread of cancer.
Throughout the 17th and 18th centuries, some believed that cancer was contagious. In fact, the first cancer hospital in France was forced to move from the city in 1779 because people feared cancer would spread throughout the city. Although human cancer, itself, is not contagious, we now know that certain viruses, bacteria, and parasites can increase a person’s risk of developing cancer.