Breast cancer and genetics

Transcription

1 Breast cancer and genetics Cancer and genes Our bodies are made up of millions of cells. Each cell contains a complete set of genes. We have thousands of genes. We each inherit two copies of most genes, one copy from our mother and one copy from our father. Genes act like a set of instructions, controlling our growth and how our bodies work. Any alteration in these instructions is called a mutation (or change). Mutations (or changes) can stop a gene from working properly. A mutation (change) in a gene can cause a genetic disorder. Genes are responsible for many of our characteristics, such as our eye colour, blood type or height. Some genes control the amount of cells and their growth in any part of the body. This control prevents cancer. If several genes of this type have changes (mutations), this control is lost, and cancer may arise. Genes tend to accumulate changes (mutations) as people grow older, so cancer is usually a disease of old age. Some people are born with a gene with a mutation (change), so that they have a tendency to get a particular type of cancer. This is familial or inherited cancer. Familial cancer is far less common than sporadic or non-inherited types of cancer. Breast cancer and genes Breast cancer is very common. Around 1 in 9 women (11%) in the UK will develop breast cancer. Most breast cancer occurs late in life and by chance. In some people the cancer is due to an inherited change (mutation) in a breast cancer gene. Is the breast cancer in my family likely to be inherited? Most breast cancers occur by chance. It is important to note that, even in families with 2 or 3 women affected by breast cancer, this may be due to chance. Only 5-10% (or fewer than one in ten) of all breast cancers are thought to be due to an inherited change (mutation) in one of the breast cancer genes. To date, two genes for familial breast cancer have been identified. These are called BRCA1 and BRCA2. Breast cancer is more likely to be caused by a gene with a mutation (change) in someone who has a strong family medical history. For example, if:

2 Two or more close blood relatives (parent, brother, sister, child) on the same side of the family are affected with breast cancer. 2 A member of the family develops breast cancer young, before 40 years of age. A member of the family has had two types of cancer. For example, cancer of the breast and cancer of the ovary. A family has a male relative with breast cancer. Both cancer of the breast and cancer of the ovary occur on the same side of the family (either the mother s family or the father s family). Women who have only one close relative affected by breast cancer (after age 40) can be reassured that it is unlikely to be due to an inherited gene mutation (change). These women would not usually be offered early breast screening. If there is a breast cancer gene mutation (change) in my family, will I inherit it? Everyone inherits two BRCA1 genes, one from each parent. The same is true for the BRCA2 gene. Either a normal breast cancer gene or a breast cancer gene with a mutation (change) can be inherited from either parent. If a parent has a gene with a change (mutation), there is a 50:50 (1 in 2) chance that it will be passed on, for each child. There is also a 50:50 (1 in 2) chance that it will not be passed on, for each child. These chances apply whether the child is a boy or a girl. What are the chances of developing breast cancer for someone who carries a BRCA gene with a mutation (change)? Not everyone who inherits a BRCA gene with a mutation (change) will go on to develop cancer. BRCA gene mutations (changes) increase the likelihood of developing cancer. If a woman is a proven carrier of a BRCA1 gene change (mutation), the chance that she will develop breast cancer may be as high as 80% over her lifetime. She also has an increased risk of developing cancer of the ovary (ovarian cancer). BRCA2 gene changes (mutations) also give an increased risk of breast cancer, of around 60% over a person s lifetime. They also give an increased risk of developing cancer of the ovary. Any person in the family who does not inherit the BRCA1 or BRCA2 gene change (mutation) is at the same risk of developing cancer as a person in the general population, and does not need additional breast screening. There is a much lower risk to men s health. It is helpful to be aware of the possibility of male breast cancer, but to remember that it is rare. Male carriers of a BRCA2 gene change (mutation) may have a higher risk of prostate cancer.

3 3 Will I be offered breast screening? All women, especially those with a family medical history of breast cancer are advised to practice breast awareness, which involves self-examination, and looking for any changes in the breasts. It is best to do this frequently, at different times of the menstrual cycle. Women between the ages of 50 and 70 are eligible for 3-yearly mammograms as part of the National Breast Screening programme. A mammogram is a special breast check-up. Women over 70 are eligible for screening on request. Women who are thought to be at a significantly increased risk of developing breast cancer will usually be offered annual mammography at an earlier age, depending on current guidelines. Women over 50 who are in high-risk groups may be offered mammography more frequently than in the National Breast Screening Programme. Preventative surgery to remove healthy breast tissue (prophylactic mastectomy) has been considered by some women. This is very much an individual decision and needs careful consideration. If a woman wishes to consider this option, she can be referred to a breast surgeon for further discussion. Can I have a test to see if I carry a breast cancer gene with a mutation (change)? This is available only for a small number of families who have a significant history of cancer of the breast, or cancer of the ovary, or both these cancers. First, it is necessary to take a blood sample from a living relative who has been affected by breast cancer. If a gene change (mutation) is found in this sample, then it may be possible to offer a genetic test to other family members, should they wish it. BRCA1 and BRCA2 gene analysis is technically difficult and time-consuming. If a gene mutation (change) is not found, either: A gene change (mutation) may be present but it was not possible to detect it, or The change (mutation) may be in another gene which it is not possible to test at present, or There is no inherited gene change (mutation) in the family.

4 4 Are there any factors which may affect my risk? Not all gene carriers develop cancer, therefore other factors must be involved. The increased chance of developing breast cancer for women who take the contraceptive pill is thought to be small, especially when the pill used for a limited time, for example 5 years. This risk is reduced after the contraceptive pill is stopped. The risks associated with longer-term use are more widely debated. The increased risks associated with hormone replacement therapy (hormone replacement therapy, HRT in English, hormone replacement therapy) are small if it is used for a limited period of time. Prolonged use of hormone replacement therapy (for longer than five years) is not recommended. Breast-feeding is thought to give some protection against breast cancer. A diet which includes plenty of fresh fruit and vegetables and less red meat and fats is thought to be beneficial. Being overweight may increase the risk of breast cancer. Drinking large amounts of alcohol may increase the risk of breast cancer. Taking regular exercise reduces the risk of breast cancer. [Where can I get more information about inherited breast cancer? Our knowledge of cancer genetics is growing rapidly, and the information given is a brief summary of what is currently known. Further information can be obtained from your local regional genetics centre or from these addresses: CancerBACUP 3 Bath Place, Rivington St., London EC2A 3JR Telephone: info@cancerbacup.org Web: Breakthrough Breast Cancer 3 rd Floor, Kingsway House, 103 Kingsway, London WC2B 6QX Telephone: info@breakthrough.org.uk Web: The Genetic Interest Group Unit 4D, Leroy House, 436 Essex Rd., London N1 3QP Telephone: mail@gig.org.uk Web: This information prepared July 2005 Ref 4

5 5 Glossary (difficult words and their meanings): Breast Cancer and Genetics This glossary is intended only to explain terms used in the information: Breast cancer and genetics. Words shown in bold are defined elsewhere in the glossary. BRCA1, BRCA2. Names of two genes associated with breast cancer. A person who has a mutation (change) in either of these genes has an increased likelihood of developing cancer compared to someone without the mutation (change). cancer. Abnormal growth of cells. carrier. Someone who has a mutation (change) in a BRCA gene but does not have cancer. Some carriers do not develop cancer. Carriers are at high risk of developing cancer cell. The human body is made up of millions of cells, which are like building blocks. There are many specialised types of cells. These include skin cells, brain cells, and blood cells. Cells in different parts of the body look different and do different things. Every cell (except for eggs in women and sperm in men) contains all the body s genes. contraceptive pill. Tablet which can be taken regularly by a woman wishing to avoid pregnancy, or as prescribed by a doctor. gene. Information needed for the body to work, stored in a chemical form. Changes or mutations in genes alter the information and this can change how the body works. Most genes are in pairs: one from the mother, one from the father. (As an analogy: a gene is like a story in a book, a change or mutation in a gene is like a missing or extra letter in a word in the story). genetic. Caused by genes, concerning genes. hormone. Chemical made by the body to control a particular task, such as making of breast milk, or regulating the menstrual cycle. Hormones may also be given as medicines. hormone replacement therapy, HRT. Particular hormones which may be given to a woman as medicines, when her body is no longer able to produce those hormones. mammogram. A special x-ray picture of the breast. mastectomy. Operation to remove a breast. menstrual cycle. The monthly changes in a woman who menstruates (has periods), including the time between one menstruation (period) and the next. mutation. A change in a gene. Some mutations are not harmful. Sometimes when a gene is changed, its information is altered so it does not work properly. (As an analogy: a change or mutation in a gene is like a missing or extra letter in a word in a story).

6 6 ovary. Part of a woman s body that produces eggs. prophylactic. Preventative. Something done to prevent a future event. prophylactic mastectomy. Removal of a breast in someone who does not have cancer, but has a gene change (mutation) which increases her risk. Removal of a breast in someone who does not have cancer and does not have a known gene change (mutation), but has a very strong family medical history which increases her risk. prostate. A part of a man s body, inside his body. It surrounds the inner end of the tube through which he passes water. sporadic. Not familial or inherited. Occurring by chance. This glossary is intended only for use by patients and families, with the genetic information to which it refers. This edition prepared in July 2005 Ref Glossary 4