What are the different theories to explain Cancer Development?

From the earliest times, physicians have wondered about the cause of cancer. The Egyptians blamed Gods for the development of cancers. Several theories were proposed by different scientists to explain the cause for cancers. Some of them are as follows.

Humoral theory:

Hippocrates believed that the body contained four humors (body fluids) – blood, phlegm, yellow bile, and black bile. A balance of these fluids resulted in a state of health. Any excesses or deficiencies caused disease.

An excess of black bile collecting 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 unchallenged through the middle Ages for over 1300 years.

During this period, the study of the body, including autopsies, was prohibited for religious reasons, thus limiting knowledge.

Lymph Theory:

Among theories that replaced the humoral theory of cancer was cancer’s formation by another fluid – lymph.

Life was believed to consist of continuous and appropriate movement of the fluid parts through solids. Of all the fluids, the most important were blood and lymph.

Stahl and Hofman theorized that the cancer was composed of fermenting and degenerating lymph varying in density, acidity and alkalinity. The lymph theory gained rapid support.

John Hunter (1723-1792) 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 was of the opinion that cancer cells did not arise from normal cells.

Muller proposed that cancer cells arose from budding elements (blastema) between normal tissues. Muller’s 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 chronic irritation as the cause of cancer, but he falsely believed that cancers “spread like a liquid.” A 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, cancer was thought by some to be caused by trauma. This belief was maintained despite the failure to cause cancer in experimental animals by injury.

Parasite Theory:

In 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 of the fear of the spread of cancer throughout the city.

A Nobel Prize was wrongly awarded in 1926 for scientific research documenting stomach cancer being caused by worms. With the inability to confirm this research, scientists lost interest in the parasite theory.