All types of cancer involve genes. Cancer begins when cells grow uncontrollably and this growth is controlled or not controlled by instructions from the genes. When genes are damaged, or mutated, these instructions may be incorrect or incomplete and lead to tumor formation.

Genetic testing is used by physicians to predict or diagnose genetic disorders that are caused by gene mutations. The tests typically use blood samples, but also may be conducted with bone marrow, skin or other tissues. These tests can analyze a patient's:

• DNA (deoxyribonucleic acid). The genetic material that houses instructions for all of the body’s chemical processes.
  
  
• RNA (ribonucleic acid). The genetic material that converts the information stored in DNA into proteins.
  
  
• Proteins. Molecules composed of amino acids that serve as the basis of body structures, such as hair and skin.
  
  
• Chromosomes. Rod-shaped elements in the nucleus of each cell. Chromosomes contain DNA and proteins that comprise the genes that carry hereditary information.
  
  
• Metabolites. Any product of metabolism.

Genes are inherited from both the mother’s egg and the father’s sperm. Genetic tests are most often used to determine if an individual has inherited a gene alteration known to be associated with cancer, or to confirm a suspected genetic mutation.

Genes provide the basic blueprint for an individual’s development, growth and bodily functions. Everything from eye color to height and body build is largely controlled by genetics, although environmental factors also play a role in the development of physical characteristics.

Genes are normally reproduced whenever cells divide, with new cells sharing the same genetic makeup as their predecessors. However, in some cases, an error occurs that causes the new gene to have an abnormality – or mutation – in its genetic code. Mutations can have harmful, beneficial or neutral effects on health. It is these mutations that may eventually lead to cancer. Scientists have not yet identified all of the genes in the human body (human genome) or the purpose of each gene.

In most cases, genetic mutations are due to the aging of the cell, or environmental or behavioral factors. These are known as acquired mutations. However, 5 to 10 percent of cancers are caused by hereditary mutations, according to the American Cancer Society (ACS). Diseases such as cancer may occur if a person has a dominant disease gene, two recessive genes for the disease, or mutations that interact with each other or the environment. The body has two main types of genes that influence cancer risk:

• Oncogenes are acquired or hereditary mutations that cause normal cells to grow out of control. In normal function, these genes direct cell growth. When their DNA is damaged or mutated, they stay “turned on” and tell a cell to continue to grow without stopping. In such situations, the oncogene may promote the growth of a tumor.  
  
  
• Tumor suppressor genes are normal, helpful genes that control cell division, repair damaged DNA and destroy cells that cannot be repaired. Acquired or hereditary mutations can inactivate tumor suppressor genes, which means they do not stop cell growth and a tumor may develop. Inherited abnormalities of tumor suppressor genes cause many of the hereditary cancers.

Researchers have identified more than 100 oncogenes and about 30 tumor suppressor genes and continue their attempts to discover more of these genes. Scientists are only beginning to understand the complexity of the genetic aspects of cancer. Cancers associated with congenital (inborn)  genetic disorders are grouped under the heading hereditary cancer syndromes. They include:

• Hereditary breast and ovarian cancer (HBOC). About 5 to 10 percent of breast cancers are associated with mutated genes, primarily the BRCA1 and BRCA2 genes. Two other genes, CHEK2 and TP53, have also been linked to breast cancer. The presence of these genes indicates an increased risk of ovarian cancer as well. Women with a BRCA1/2 mutation are 3 to 7 times more likely to develop breast cancer than those without the gene alteration. In the general population, a woman has 1.7 percent chance of developing ovarian cancer in her lifetime. If a woman has a BRCA1/2 gene mutation, the risk increases to 16 to 60 percent.
  
  
• Familial prostate cancer.  Male carriers of the two main gene mutations (BRCA1/2) involved in hereditary breast cancer have three to four times the risk of developing prostate cancer. Other gene mutations, including the PITX2 gene. have also been implicated in prostate cancer,
  
  
• Hereditary causes of colorectal cancer, including hereditary nonpolyposis colon cancer (HNPCC) and familial adenomatous polyposis (FAP). These conditions, characterized by polyps that may become malignant, are estimated to account for up to 15 percent of cases of colorectal cancer.
  
  
• Familial melanoma. Several melanoma-predisposing autosomal dominant genes have been identified. An estimated 5 to 7 percent of people with melanoma come from genetically high-risk families.
  
  
• Neurofibromatosis. Type 1 neurofibromatosis affects one person in 4,000 and involves skin discoloration and tumors that become malignant in up to 5 percent of cases. Type 2 affects one person in 50,000 and often affects the acoustic nerve.
  
  
• Fanconi’s anemia. An autosomal recessive (health effect of mutation is caused only when copies of the mutation are inherited from both parents) condition associated with about 20 percent of cases of childhood aplastic anemia. It is more common in Ashkenazi Jews.

Even in cancers that can be linked to environmental conditions, such as exposure to tobacco smoke or radiation, the environment damages the tissue and genetic material to initiate the tumor growth. The genetic risk associated with cancers lies in the inheritance or mutation of genes that make a person more likely to develop a certain type of cancer. In this sense, all cancers are genetic. Some types of cancer can occur in families with above-average frequency. However, this does not mean a hereditary mutation is involved. Genetic mutations can harm, have no effect on or even help a person’s health. The cells usually but not always recognize and repair acquired mutations.

Recently, researchers have completed a “map” of the genes associated with breast and colon cancer tumors. After analyzing more than 13,000 genes from tumors, the study showed that each type of cancer had about 100 different genes with mutations. Continuing research to identify which mutations affect cancer may provide information about effective treatment and new types of therapies to repair the gene damage or stop the progress of the cancer.

Patients may want to consider genetic testing if they have a:

• Family history of cancer, especially:
  
  
• Clustering of the same type of cancer in close relatives (parents, siblings, children)
  
  
• Two or more primary cancers in one relative
  
  
• Patterns of cancer in the family that are associated with a known cancer syndrome or with other diseases
  
  
• Previous individual history of cancer
  
  
• Concerns about family members being at risk for cancer

This information may be used to help determine whether a family may have a hereditary cancer syndrome, what the most likely diagnosis is if a syndrome is indicated, and how the genetic traits are passed down in the family (dominant, recessive or X-linked). Answering these questions can help individuals make a more informed decision on whether to undergo genetic tests and genetic counseling.

Depending on the type of cancer, patients who receive positive genetic test results have several options. These include:

• Screening at earlier age
  
  
• More frequent screening schedule
  
  
• More in-depth tests recommended for high-risk patients
  
  
• Taking preventative medications (e.g. hormone-blocking drugs)
  
  
• Making certain lifestyle changes (e.g. changing an unhealthy diet or quitting smoking)
  
  
• Having preventative surgery, such as mastectomy  for women with a gene mutation for breast cancer