Genetics of Cancer
★Your genetic makeup may have an effect on treatment options available to you for ovarian cancer. And, understanding hereditary cancer can help increase awareness of risk factors in your family.
from National Institutes of Health (NIH)
“Gene: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein.”
Definition: Gene Mutation
from Genetics Home Reference, National Library of Medicine (NLM), National Institutes of Health (NIH)
“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. Mutations range in size; they can affect anywhere from a single DNA building block (base pair) to a large segment of a chromosome that includes multiple genes.
Gene mutations can be classified in two major ways:
Hereditary mutations are inherited from a parent and are present throughout a person’s life in virtually every cell in the body. These mutations are also called germline mutations because they are present in the parent’s egg or sperm cells, which are also called germ cells. When an egg and a sperm cell unite, the resulting fertilized egg cell receives DNA from both parents. If this DNA has a mutation, the child that grows from the fertilized egg will have the mutation in each of his or her cells.
Acquired (or somatic) mutations occur at some time during a person’s life and are present only in certain cells, not in every cell in the body. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation.”
Hereditary Cancer: Background Information
from Cleveland Clinic Genomic Medicine Institute
“Cancer arises from the uncontrolled growth of cells. Cells are the units that make up our tissues and organs (for example, our skin, lungs and brain), which in turn make up our entire body. When cells are doing their job well, they know when to grow and when to stop growing. Cells contain genes. Genes are the instructions that tell cells how to function properly, like when to grow and when to stop growing. Cancer is caused by harmful changes in genes, called mutations. These mutations cause the cell to grow without control, and eventually become a cancer.
Most cancers are sporadic – they are not inherited and cannot be passed to your children. Because cancer is common, some families may have a few members affected with sporadic cancers just by chance. Sporadic cancers may be the result of environmental exposures. Sporadic cancer may also be due to mutations that occur in genes by chance when a cell divides. Since these mutations occur only in the cancer cells, they cannot be passed on.
Sometimes cancers cluster in families. In these cases, more cancers are occurring than would be expected by chance, yet they do not appear to be clearly hereditary (able to be passed on within the family). It is possible that interactions are occurring between genes and the environment or among several genes that contribute to the development of these cancers. This type of moderately increased cancer risk can be called a “familial” risk.
About 5-10% of cancers are believed to be hereditary. Hereditary susceptibility to cancer can be inherited and passed on within a family. Individuals who inherit a mutation in a cancer susceptibility gene have a much greater chance for developing cancer. However, not everyone with a cancer susceptibility gene mutation will develop cancer.
Cancer susceptibility gene mutations can be inherited from, and passed on to, men as well as women. Almost all genes come in pairs. One gene copy of each pair is inherited from the father and the other gene copy is inherited from the mother. Therefore, if a parent has a gene mutation associated with cancer susceptibility, each of his/her children has a 50%
(1 in 2) chance of inheriting the gene mutation. Each child also has a 50% chance of inheriting the working copy of the gene, in which case his/her cancer risk would be no higher than that of the general population.
Features suggesting hereditary cancer include:
• early ages of cancer diagnoses (i.e. breast cancer before age 50)
• two or more relatives with the same type of cancer, on the same side of
• several generations affected by cancer
• multiple primary cancers in one individual (including breast and ovarian
cancer or bilateral breast cancer)
• male breast cancer
• clustering of cancers which are known to be genetically related (such as
breast and ovarian cancer, or colon and uterine cancer)
• the presence of certain features which are known to be associated with
hereditary cancer (such as moles and melanoma, or polyps and colon