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About Cancer and Genetics

Description of Genetics

Cancers develop because of alterations, or mutations, in genes that normally promote controlled cell growth. Most cancers are caused by mutations that occur only in the tissue that is affected by the cancer.

Description of Genes

Each cell in your body contains about 25,000 genes, which determine your hair color, your height, and other characteristics that make you unique.

Autosomal Dominant Inheritance

A mutation is a change in a gene that prevents it from working properly. We inherit mutations from our parents in specific ways, one of which is called autosomal dominant inheritance.

Autosomal Recessive Inheritance

This type of genetic inheritance means that both copies of the gene must have a mutation for a person to have the trait. One copy of the mutation is inherited from the mother, and the other from the father. A person who has only one recessive gene mutation is a "carrier" for the trait or disease, but he or she does not have any health problems from carrying this one mutation.

X-Linked Inheritance

X-linked inheritance means that the gene alteration causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes, and males have one X and one Y. Mutations in X chromosome genes can be recessive or dominant.

Multifactorial Inheritance

Multifactorial inheritance means that many factors are involved in causing a health problem. The factors are usually both genetic and environmental, where a combination of genes from both parents, in addition to unknown environmental factors, produce the trait or condition.

Features of Inherited Cancers

A family medical history helps determine whether relatives have an increased chance of developing specific types of cancer, how great the risk of cancer might be, and whether genetic testing might be useful.

Genetic Services for Cancer Diagnosis: When, Where, How

If you have a family history of multiple cases of the same or related types of cancer, you may need genetic counseling. Generally, you can find genetic counseling and other genetic services at large hospitals or medical centers.

How Genes Cause Cancer

Genes that have alterations, or mutations, can cause cells to become cancerous. Some mutations are inherited and others are "acquired," occurring by chance over time.

Genetics: Breast and Ovarian Cancer

Peutz-Jeghers Syndrome

People with this syndrome have dark moles around the mouth, nose, and eyes, as well as multiple polyps in the intestines.

Li-Fraumeni Syndrome

Li-Fraumeni syndrome raises the risk for breast cancer and many other types of cancer.

Genetics: Colorectal Cancer

Familial Adenomatous Polyposis (FAP)

FAP is a syndrome characterized by a large number of benign polyps in the colon and rectum. Without treatment, a person with FAP has a nearly 100 percent risk of colorectal cancer.

Other Colorectal Cancer Syndromes

Several rare syndromes raise the risk for colorectal cancer. These disorders include Turcot syndrome, Peutz-Jeghers syndrome, juvenile polyposis coli, and MYH-associated polyposis.

Genetics: Other Cancers

The Genetics of Prostate Cancer

The majority of cases of prostate cancer are sporadic, which means that one person in the family developed prostate cancer by chance at a typical age for this cancer. In these cases, other male relatives have little to no increased risk of developing prostate cancer.

The Genetics of Lung Cancer

Ninety percent of lung cancers are caused by smoking, but not everyone who smokes will develop lung cancer. Researchers believe that normal genetic variations, known as polymorphisms, may make some people more likely to develop lung cancer if they smoke.

The Genetics of Skin Cancer

Up to half of all Americans 65 and older will have at least one bout of skin cancer. The most common types of skin cancer in the United States are basal cell and squamous cell carcinomas. These are generally the result of sun exposure.

Medullary Thyroid Cancer (MTC)

This rare type of thyroid cancer has several forms, depending on the mutations that cause it. Most cases of medullary thyroid cancer, though, are sporadic—they occur without any family history of thyroid cancer.

Von Hippel-Lindau Syndrome

VHL is a rare genetic disorder marked by an increased risk of developing benign tumors in the brain, spine, retina, and adrenal gland, and cancerous tumors in the kidney.

Genetic Testing

Types of Genetic Testing

Chromosome studies may be performed when a child is born with multiple birth defects or when people have certain types of leukemias and lymphomas, to look for specific chromosome rearrangements associated with these types of cancers. Direct DNA studies look directly at the gene in question for an error.

Before Undergoing Genetic Testing for Cancer

Testing methods vary from laboratory to laboratory and may affect the likelihood that the lab will identify a mutation in the gene if one is present. Different laboratory studies have the ability to detect different types of mutations. Accuracy will vary, depending upon the type of genetic testing method performed.
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