From the earliest times, physicians have puzzled over the causes of cancer. Ancient Egyptians blamed cancers on the gods.
Humoral theory
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.
Lymph theory
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.
Blastema theory
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.
Trauma theory
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.
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