Cancer is a genetic disease—that is, cancer is caused by certain changes to genes that control the way our cells function, especially how they grow and divide. These changes include mutations in the DNA that make up our genes. Genetic changes that cause cancer can be inherited from our parents. They can also arise during a person’s lifetime as a result of errors that occur during cell division or damaged DNA caused by certain environmental exposures. Cancer-causing environmental exposures can include substances such as the chemicals in tobacco smoke, radiation, or ultraviolet rays from the sun. Each patient’s cancer has a unique combination of genetic changes. As the cancer continues to grow, additional changes will occur.
How Cancer Arises
The Importance of the Chromosome
A gene is a segment of DNA containing a code used to synthesize a protein. Chromosomes are found within a cell and contain hundreds to thousands of genes. Every human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes a cell.
The Basics of DNA
There are four components which make up DNA, Adenine, Guanine, Cytosine and Thymine, (AGCT for short). Each specific component is always paired with one another (A to T and G to C). Each of these four components contains a nitrogenous base, a deoxyribose sugar, and one phosphate group. The pattern which these pairings are placed makes up a specific pattern in each of us. This specific pattern is what makes our genes different.
Mutations
A gene mutation is a permanent alteration in the DNA sequence that makes up a gene, such that the sequence differs from what is found in most people. These can affect anywhere from one base pair to an entire segment of a chromosome. These can occur due to environmental factors such as ultraviolet radiation (from the sun) or can occur if a mistake is made as the DNA copies itself during cell division as part of the cell cycle. Gene mutations are detected through genetic testing. This is the analysis of chromosomes (DNA), proteins, and certain metabolites in order to detect heritable disease-related genotypes, mutations, phenotypes, or karyotypes for clinical purposes.
The Cell Cycle
The Cell Cycle is a series of “events” that happen in a cell leading to its division and duplication of its DNA (DNA replication) to produce two baby cells.
Within the cell cycle, there are many stages:
In the first gap phases (G1), metabolic changes prepare the cell for division.
After this, the cell is moved to the Synthesis phase (S), where genetic material is duplicated. DNA synthesis replicates the genetic material and each chromosome now consists of two sister chromatids.
Next is the second gap phase (G2) is where metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis.
Last, the cell goes through the Mitosis phase (M) in which mitosis partitions the genetic material and the cell divides.
The Checkpoints
The cell cycle is controlled at three checkpoints. The quality of the DNA is assessed at the G1 checkpoint as well as damage to DNA and other external factors. If conditions are inadequate, the cell will not be allowed to continue to the S phase of interphase. Proper chromosome duplication is assessed at the G2 checkpoint. The G2 checkpoint ensures all of the chromosomes have been replicated and that the replicated DNA is not damaged before cell enters mitosis. This stage can be thought of as a “safety gap” during which a cell can check to make sure that the entirety of its DNA and other intracellular components have been properly duplicated.
In cancer, as a result of genetic mutations, this regulatory process malfunctions, resulting in uncontrolled cell growth. When cancer cells go through the checkpoints without being checked correctly, they begin to divide out of control. The cancer cells end up clumping together creating tumors.