Characteristics of Cancer Cells

Almost all types of differentiated cells can become neoplastic or can become neoplastic or cancerous. The process of cell change in which a cell loses its ability to control its rate of division, and thus becomes a tumor cell, is called cell transformation.

1. Immortalization. Normal cell cultures do not survive indefinitely. Cell cultures infected with mouse sarcoma virus can be maintained as long as nutrition is provided and overcrowding avoided.

2. Loss of contact inhibition. Normal cells in a culture stop growing when their plasma membranes come into contact with one another. The inhibition of growth after contact is called inhibition.

3. Reduced cellular adhesion. When normal cells become cancerous there is a change in the ‘stickiness’ of their cell membranes. Normal cells show stickiness or adhesiveness. When normal cells become cancerous there is a change in the ‘stickiness’ of their cell membrane. Normal cells show stickiness or adhesiveness.

4. Invasiveness. One of the most important characteristics of transformed cells is their invasiveness, i.e., the ability to invade other tissues. This invasiveness could be the result of changes in the plasma membrane and proteases released by the cells.

5. Loss of anchorage dependence. Most normal cells must be attached to a rigid substratum in order to grow. Transformed cells can grow even when they are not attached to the substratum.

6. Lower serum requirements. Growth of normal cells in a tissue culture medium requires a high concentration of serum. Some serum growth factors resemble insulin in interacting with external receptors on the cell membrane to regulate biochemical activities within the cell.

7. Selective agglutination by lectins. Lectins are proteins widely distributed in plants, particularly legumes, but are also found in some animals. In normal cells the receptors or agglutinin binding sites for lectins lie in a diffuse manner on the cell surface and are immobile.

8. Molecular changes in cell membrane components. There are several differences between the surface cell membranes of normal and transformed cells. The cell membrane consists of four main types of phospholipids, which form the lipid bilayer, with glycolipids and galycoproteins inserted into this bilayer.

9. Disorganization of the cytoskeleton. Normal cells have a cytoskeleton which consists of microtubules and microfilaments. These fibres have a regular arrangement and bring about coordinated cell movement.

10. Increase in negative surface charge of cell membrane. Comparisons of surface membrane charge by micro electrophoresis have been made between normal and malignant cells. In malignant cells anodic mobility is usually higher, indicating increase in negative surface charge.

11. Increased sugar transport. Tumor cells consume much more glucose than normal cells because they have to grow and multiply. There is a great increase in the rate of sugar transport across the surface cell membrane after transformation.

12. Appearance of virus-specific transplantation-rejection antigens. Plasma membranes of most transformed cells contain antigens which are not present in normal cells. Thus in cells transformed by adenoviruses and papovaviruses the T-antigen are always present.

13. Defective electrical communication. Electrical connections normally occur between individuals cells. In some cancer cells, however, it has been reported that such connection are defective.

14. Increased secretion of proteolytic enzymes. Large amounts of proteolytic enzymes are secreted by all types of cancer cells, except those of blood-forming tissues. The cancer secretes a protease called the cell factor.

15. Aldolases. In most mammalian tissues the enzyme aldolase exists in the form of three isozymes A, B and C.  Isozyeme A and C predominate in embryonic tissues, while in adult differentiated tissues the B isozyme is predominant.

16. Increased rate of glycolysis. This has been demonstrated by an increase in lactic acid production in cells of solid tumours. There is a corresponding increase in the uptake of glucose.