The older animals and humans have some localized growth of tissue, having cells that are closely resembled and function like normal cells. The cell adhesion and interaction molecules hold together is called the tumor of benign type. As they are surrounded by the fibrous tissues and remain stay in their original place they can be easily surgically operated. Sometimes, these benign tumors interfere normal physiological functions, if they secrete excess hormones or other substances and cause serious medical problems.
Malignant tumors are different biologically from the benign tumors. They are usually less well differentiated than normal or benign tumor cells. They synthesize specific types of proteins while some tissue-specific proteins are not synthesized and thus the normal function of that tissue is hampered. The cells divide rapidly, having high nucleocytoplasmic ratios with prominent nucleoli. The cell adhesive substances become abnormal, as a result the cells become loose, the blood vessels in the tissue are changed. The cells then undergo metastasis.
The cancerous cells have some key proteins which make the cells malignant.
These properties are:
1. They disobey the external and internal regulatory systems in the cell proliferation mechanism.
2. They tend to avoid apoptosis.
3. They disobey the programmed limitations of proliferation, escaping replicative senescence and avoiding differentiation.
4. They are genetically unstable.
5. They acquire metastatic properties.
6. They can survive and proliferate at foreign sites.