Modern knowledge and cancer cause
By the middle of the 20th century, scientists had the instruments they needed to work on some of the complex problems of chemistry and biology that remained unsolved. James Watson and Francis Crick, who received a Nobel Prize in 1962 for their work, had discovered the exact chemical structure of DNA, the basic material in genes.
DNA was found to be the basis of the genetic code that gives orders to all cells. After learning how to translate this code, scientists were able to understand how genes worked and how they could be damaged by mutations (changes or mistakes in genes). These modern techniques of chemistry and biology answered many complex questions about cancer.
Scientists already knew that cancer could be caused by chemicals, radiation, and viruses, and that sometimes cancer seemed to run in families. But as the understanding of DNA and genes increased, they learned that it was the damage to DNA by chemicals and radiation, or the introduction of new DNA sequences by viruses that often led to the development of cancer. It became possible to pinpoint the exact site of the damage on a specific gene.
Scientists discovered that sometimes defective genes are inherited, and sometimes these inherited genes are defective at the same points that chemicals exerted their effect. In other words, most of the things that caused cancer (carcinogens) caused genetic damage (mutations), these mutations led to abnormal groups of cells (called clones), the mutant clones evolved to even more malignant clones over time, and the cancer progressed by more and more genetic damage and mutations. Normal cells with damaged DNA die; cancer cells with damaged DNA do not. The discovery of this critical difference answered many questions that had troubled scientists for many years.
Oncogenes and tumor suppressor genes
During the 1970s, scientists discovered 2 particularly important families of genes related to cancer: oncogenes and tumor suppressor genes.
Oncogenes are mutated forms of genes that cause normal cells to grow out of control and become cancer cells. They are mutations of certain normal genes of the cell called proto-oncogenes. Proto-oncogenes are the genes that normally control how often a cell divides and the degree to which it differentiates (or specializes).
Tumor suppressor genes are normal genes that slow down cell division, repair DNA errors, and tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don’t work properly, cells can grow out of control, which can lead to cancer.
It may be helpful to think of a cell as a car. For it to work properly, there need to be ways to control how fast it goes. A proto-oncogene normally functions in a way that is similar to a gas pedal — it helps the cell grow and divide. An oncogene could be compared to a gas pedal that is stuck down, which causes the cell to divide out of control. A tumor suppressor gene is like the brake pedal on a car. It normally keeps the cell from dividing too quickly just as a brake keeps a car from going too fast. When something goes wrong with the gene, such as a mutation, cell division can get out of control.
Slowly, medical scientists are identifying the oncogenes and tumor suppressor genes that are damaged by chemicals or radiation and those that, when inherited, can lead to cancer. For example, the 1990s discovery of 2 genes that cause some breast cancers, BRCA1 and BRCA2, represents considerable promise because these genes can be used to identify people who have a higher probability of developing breast cancer.
Other genes have been discovered that are associated with some cancers that run in families, such as cancers of the colon, rectum, kidney, ovary, thyroid, pancreas, and skin melanoma. Familial cancer is not nearly as common as spontaneous cancer. It is less than 15% of all cancers. Still, it is important to understand these cancers because with continued research in genetics we may be able to identify people at very high risk.
Once researchers recognized the importance of specific genetic changes in cancer, they soon began working to developtargeted therapies (drugs or substances that interfere with specific molecules) to overcome the effects of these changes in tumor suppressor genes and oncogenes.
source : cancer.org