Cancer cells don't stop growing when one layer of cells touches another layer, like normal cells do. Some cancer cells resemble fetal and neonatal cells in that they divide quickly, and you don't know what kind of cell they are going to be until they begin to differentiate into the specialized cells that make up the arms, the legs, the eyes, the gastrointestinal tract, and so on. Cancer cells, however, do not differentiate. Contrary to popular belief, most cancer cells do not grow faster than normal cells (fetal cells being normal cells).

All types of differentiated cells 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 tumour cell, is called cell transformation .The cancerous cell generally retains the structural and functional characteristics of the normal cell type from, which it is derived. Thus cancerous cells of the thyroid gland continue to secrete thyroxin. Neoplastic cells, however, differ from their normal counterparts in several respects.

1. cancer cells are immortal

Normal cell cultures do not survive indefinitely. Human cell cultures die after about 50 generations, and chicken cell cultures have a much shorter life expectancy. As long as they receive nutrients, cancer cells can live and multiply without end.

2. contact inhibitions

When two normal cells come into contact, one or both will stop moving and then begin to move in another direction. This inhibition of growth after contact is caned contact inhibition. Normal cells in a culture stop growing when their plasma membranes come into contact with one another.
Cancer cells don't stop growing when one layer of cells touches another layer, like normal cells do. Some cancer cells resemble fetal and neonatal cells in that they divide quickly, and you don't know what kind of cell they are going to be until they begin to differentiate into the specialized cells that make up the arms, the legs, the eyes, the gastrointestinal tract, and so on.

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. If grown in a nutrient medium kept in a glass vessel, the cells stick to the glass rather than float in the medium.
Transformed cells show a decreased adhesiveness, and if grown in solid media stick to each other less than do normal cells.

4. Exhibit drug resistance

Cancer cells can develop a tolerance for the drugs that are used to treat them.Some bacteria show this same characteristic; they can become tolerant to certain antibiotics and drugs used to control them.

5. Invasiveness.

One of the most important characteristics of transformed cells is their invasiveness, i.e. the ability to invade other tissues.