The incidence of cancer has increased to such an extent that every second family now has at least a few members diagnosed with it. The causes of cancer largely include heavy smoking and drinking, sedentary lifestyle, improper diet, obesity, environmental factors etc. Besides these, cancer can also be hereditary in nature. However, hereditary cancer genes account for a very small percentage of all cancers. Often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself. Only about five per cent of all cancers are inherited, resulting directly from gene defects inherited from a parent.
At times, when there are numerous cases of cancer occurring in a family, it is most often by chance or maybe because of the family members’ exposure to a common toxin, such as cigarette smoking. There are very less chances of acquiring cancers by an inherited gene mutation. However, there are certain things like cases of an uncommon or rare type of cancer, cancers occurring at younger ages than usual and more than one type of cancer in a single person, more than one childhood cancer in a set of siblings that are more likely to cause cancer in a family through an abnormal gene.
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J B Sharma
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Cancer in a close relative, like a parent or sibling, is much more a cause for concern than cancer in a more distant relative. Even if the cancer develops from a gene mutation, the chance of it passing on to a person gets lower with more distant relatives. Above all, what also matters is the type of cancer. More than one case of the same rare cancer is more worrisome than cases of a more common cancer. And having the same type of cancer in many relatives is more concerning than if it is several different kinds of cancer. Still, in some family cancer syndromes, a few types of cancer seem to go together. For e.g., breast cancer and ovarian cancer run together in families with hereditary breast and ovarian cancer syndrome (HBOC). Colon and endometrial cancers tend to go together in a syndrome called hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome.
Age is again an important factor when a person is diagnosed with cancer. For e.g., colon cancer is rare in people under the age of 30. Having two or more cases in close relatives of similar age group could be a sign of an inherited cancer syndrome. On the other hand, prostate cancer is very common in elderly men, so if both a father and his brother were found to have prostate cancer when they were in their 80s, it is less likely to be due to an inherited gene change. However, when many relatives share a similar type of cancer it is important to notice if the cancer could be related to smoking. For e.g., lung cancer is commonly caused by smoking, so many cases of lung cancer in a family of heavy smokers are more likely to be due to smoking than to an inherited gene change.
Hereditary cancers are majorly of four types.
- Breast cancer
Breast cancer There are concerns over breast cancer running in the family since a woman having a first-degree relative with breast cancer is about twice as likely to develop breast cancer compared to a woman without a family history of this cancer. Still, most cases of breast cancer, even those in close relatives, are not part of a family cancer syndrome caused by an inherited gene mutation.
Chances of inheriting a form of breast cancer are higher when younger or when they have more relatives with the disease. Inherited breast cancer can be caused by several different genes, but the most common are BRCA1 and BRCA2 in which inherited mutations cause hereditary breast and ovarian cancer syndrome (HBOC).
For women with a strong family history of breast cancer, we must prescribe them to undergo genetic counselling to estimate their risk for inherited breast cancer. If a mutation is present after the tests, the woman has a high risk of developing breast cancer. In such cases mammography must be conducted at an age younger than 40 along with special breast cancer screening tests.
- Colon Cancer
Colon Cancer It is caused by a disease called familial adenomatous polyposis (FAP). People with this disease start getting colon polyps by their teen years, and over time may have hundreds of polyps in their colon. If left alone, at least one of these polyps becomes cancer. The gene for this syndrome is called APC, and testing for mutations in this gene is available. If FAP is diagnosed early in life, a surgery to remove this colon helps stop the cancer from developing.
Meanwhile, the hereditary non-polyposis colorectal cancer (HNPCC), or Lynch syndrome, which is the most common inherited syndrome of increasing a person’s risk for colon cancer, carries a high risk of colorectal cancer. Most of these cancers occur before the age of 50. HNPCC also leads to a high risk of endometrial cancer in women, besides cancer of the ovary, stomach, small intestine, pancreas, kidney, brain, urethra and bile duct.
HNPCC is caused by mutations in one of the DNA repair enzyme genes MLH1, MSH2, MSH6, PMS1, or PMS2. Mutations in these genes can be found through genetic testing. For someone who is carrying an HNPCC gene mutation, they should start colonoscopy screening at an early stage. Some people even have surgery to remove most of the colon to try and prevent cancer from starting. A screening can also be done for endometrial cancer whereas in some cases, uterus needs to be removed after a woman is done with bearing children.
- Childhood cancers
Childhood cancers Like adult cancers, most childhood cancers are not inherited. But there are a few types of childhood cancers that occur more often in some families. They occur due to hereditary cancer syndromes like Retinoblastoma, a childhood cancer that starts in the eye, can be caused by an inherited mutation in the tumour suppressor gene-Rb. One out of every four children with retinoblastoma carries this abnormal gene in every cell of their body. In most of these cases, this is due to a new mutation (gene change) in the sperm or egg, whereas in others, the abnormal copy of Rb is inherited from a parent. Children with the hereditary form of retinoblastoma are more likely to get tumours in both eyes. They also have an increased risk of developing other types of cancer, including cancers of the bone, brain, nasal cavities, and a type of skin cancer (melanoma).
- Li-Fraumeni syndrome
Li-Fraumeni syndrome This syndrome occurs when a person inherits a mutation in the gene for p53 (TP53, a tumour suppressor gene). People with a TP53 gene abnormality have a higher risk of childhood sarcoma, leukaemia, and brain (central nervous system) cancers. Li-Fraumeni syndrome also raises risk of cancers of the breast and adrenal glands.
Since inherited mutations affect all the cells of a person’s body, genetic testing helps in identifying the mutations. We need to recommend genetic counselling and testing to people with a strong family history of cancer. Genetic testing can be suggested to those people who have several first-degree relatives with cancer, cancers in their family that are sometimes linked to a single gene mutation, family members who had cancer at a younger age, close relatives with rare cancers that are linked to inherited cancer syndrome or a known genetic mutation in one or more family members. However, if a genetic test result turns positive, managing the risk should become a priority for us as well, besides the patient. Some of the ways to lower the risk includes prescribing chemoprevention, preventive or prophylactic surgery, and suggesting lifestyle changes.
The increasing evidence of genetic or hereditary linkage to cancer onset and development can no longer be overlooked. While genetic testing facilities are available, they should be made more accessible to individuals. Although researches are being conducted to find newer and better ways of detecting, treating, and preventing cancer in people who carry genetic mutations, but an awareness of genetic predispositions coupled with a healthy lifestyle among the individuals, will result in significant reduction in the risk of developing cancer.
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