What Is Cancer?

By Dr Ann Lee, Senior Scientist
Division of Medical Sciences, NCC

Our body is made up of billions of cells of different types, depending on the tissue or organ of origin. Under normal circumstances, these cells divide and grow in a controlled manner. However, a cell is said to become cancerous when this process of cell division occurs uncontrollably, and seemingly without restraint, resulting in a mass of cancer cells. Tumors may be classified as benign or malignant. The malignant ones are those that can spread to adjacent tissues and other parts of the body, and these are known as cancerous cells. Benign tumors do not spread or metastasize but remain localized in a single mass.

Many cancers originate from a progression of normal cells to benign growths and finally to malignant cancer cells. What then causes this progression? Defects or ‘mutations’ in cancer critical genes are known to contribute to the development of cancer. These cancer genes code for proteins that are important for processes in the cell such as the control of cell division, cell signaling, DNA repair and programmed cell death. The diagram below shows a simplified flow-chart of the progression of a normal colonic epithelial cell to a cancerous one.

How then can one tell a normal cell from a cancerous one? One important way is to look at the cells under the microscope, as normal cells and cancerous cells look different (see also ‘The Face of a Cancer Cell”, written by Pathologist, Dr. Tan Puay Hoon in this newsletter). Cancer cells also exhibit genetic changes, with some of the abnormalities being so large that by viewing stained chromosomes under the microscope, a cytogeneticist can detect changes such as extra chromosomes, losses of chromosomes, additions or losses of parts of chromosomes or even the translocation of part of one chromosome onto another chromosome. Other genetic changes occur at the molecular level, and can be discerned using special equipment such as the DNA sequencer. Examples of these genetic changes include activation of oncogenes, losses or gains of specific cancer related genes, which in turn have an impact on the proteins expressed by the cancer cells.

Multiple steps in the development of colon cancer
and examples of some genetic changes

Efforts are being made here at the Research departments in NCC to develop new tools to detect cancer cells at an earlier stage, to understand how these cancer cells evolve, multiply and spread, and to identify new cancer related genes.

Further reading
“How cancer arises” by Robert A. Weinberg.
www-biology.ucsd.edu/classes/bild10.WI05/cancer.pdf

“Untangling the roots of cancer. What causes cancer” by W. Wayt Gibbs.
Scientific American (2003), pages 56-65.
mcb.berkeley.edu/labs/duesberg/ Scientific%20American%20July%20
2003.pdf