Читать книгу Fundamentals of Cancer Detection, Treatment, and Prevention - Surya K. De - Страница 18

Cancer cells differ from normal cells (Figure 1.2) in many respects [1–3]:

Appearance: Under a microscope, normal cells and cancer cells look significantly different. Cancer cells often display much more variability in cell size, with some larger than or smaller than normal cells.

Figure 1.2 Cancer cells are less organized than normal cells and grow in an uncontrolled fashion.

Growth: Normal cells stop reproducing when enough are present. For instance, if cells are required to repair a cut in the skin, new cells are no longer produced when there are enough cells present to fill the gap. Cancer cells, however, do not stop growing and reproducing, and their continuous growth results in the formation of a tumor.

Communication: Cancer cells don't interact with other cells in the same way as normal cells. Normal cells respond to signals sent from other nearby cells to stop growing. Cancer cells do not respond to these signals.

Cell repairandcell death: Regular cells are repaired or die (in a process called apoptosis) when they are damaged or get old. Cancer cells either are not repaired or do not undergo apoptosis. The p53 gene regulates cell repair and apoptosis. When this gene is mutated or inactivated, a tumor begins.

Stickiness: Normal cells produce substances that keep them cohesive within a group, as opposed to cancer cells, which do not produce these substances and can therefore spread to other body locations via the bloodstream or lymphatic system.

Ability to metastasize (spread): Normal cells remain in the same area of the body where they serve a particular function, e.g. kidney cells remain in the kidneys. Due to their lack of cohesion, cancer cells are able to move through the bloodstream and lymphatic system to other locations of the body. In these new locations, they have the ability to metastasize, forming tumors distant from the original tumor.

Rate of growth: Normal cells reproduce themselves in a controlled, orderly process, but cease reproducing when enough cells are present. Cancer cells reproduce at abnormal rates, often rapidly and with no stopping mechanism.

Maturation: Normal cells mature with age, whereas cancer cells remain immature and continue to reproduce unchecked before they are fully mature.

Evade the immune system: The human body's immune system is a network of organs, tissues, and specialized cells that keeps the body protected from infections and other harmful conditions. When normal cells become damaged, the immune system identifies and removes them. Cancer cells are able to evade removal by the immune system, resulting in the formation of tumors.

Energy source: In the presence of oxygen, normal cells produce most of their energy supply. Cancer cells have changed, however, and are able to produce energy without oxygen. This capacity to generate energy for growth and survival without oxygen (a condition found inside a tumor) enables cancer cells to thrive where normal cells die.