Odds Of Getting Cancer

Family Cancer Syndromes

Cancer is such a common disease that it is no surprise that many families have at least a few members who have had cancer. Sometimes, certain types of cancer seem to run in some families. Sometimes, this is because family members have certain risk factors in common, such as smoking, which can cause many types of cancer. It can also be due in part to other factors, like obesity, that tend to run in families and influence cancer risk.

But in some cases the cancer is caused by an abnormal gene that is being passed along from generation to generation. Although this is often referred to as inherited cancer, what is inherited is the abnormal gene that can lead to cancer, not the cancer itself. Only about 5% to 10% of all cancers result directly from gene defects (called mutations) inherited from a parent. This document focuses on those cancers.

DNA, genes, and chromosomes

Cancer is a disease of abnormal gene function. Genes are pieces of DNA (deoxyribonucleic acid). They contain the instructions on how to make the proteins the body needs to function, when to destroy damaged cells, and how to keep the cells in balance. Your genes control things such as hair color, eye color, and height. They can also affect your chance of getting certain diseases, such as cancer.

Every cell in your body has all of the genes you were born with. Although all cells have the same genes and chromosomes, different cells (or types of cells) may use different genes. For example, muscle cells use a different set of genes than skin cells use. The genes that the cell doesn't need are turned off and not used. The genes that the cell is using are activated or turned on.

An abnormal change in a gene is called a mutation. The 2 types of mutations are inherited and acquired (somatic).

• An inherited gene mutation is present in the egg or sperm that formed the child. After the egg is fertilized by the sperm, it created one cell called a zygote that then divided to create a fetus (which became a baby). Since all the cells in the body came from this first cell, this kind of mutation are in every cell in the body (including eggs or sperm) and so can be passed on to the next generation.
• An acquired (somatic) mutation is not present in the zygote, but is acquired some time later. It occurs in one cell, and then is passed on to any new cells that are the offspring of that cell. This kind of mutation is not present in the egg or sperm, and so cannot be passed on to the next generation. Somatic mutations are much more common than inherited mutations. Most cancers are caused by acquired mutations.

You have 2 copies of most genes – one from each parent. When someone has inherited an abnormal copy of a gene, their cells already start out with one mutation. If the other copy of the gene stops working (because of an acquired mutation, for example), the gene can stop functioning altogether. When the gene that stops working is a cancer susceptibility gene, cancer can develop. Some cancer susceptibility genes function as tumor suppressor genes. Tumor suppressor genes are normal genes that slow down cell division, repair DNA mistakes, or tell cells when to die (a process known as apoptosis or programmed cell death). When tumor suppressor genes don’t work properly, cells can grow out of control, which can lead to cancer. Many family cancer syndromes are caused by inherited defects of tumor suppressor genes.

Someone who isn’t born with a bad copy of a gene would have to acquire 2 different mutations for that gene not to work. Acquiring 2 mutations in the same gene takes longer than acquiring one, which is why cancers that are caused by inherited gene mutations tend to occur earlier in life than cancers of the same type that are not.

More information about gene changes that can lead to cancer can be found in our document Genes and Cancer.

Family cancer syndromes - when should I worry?

When many cases of cancer occur in a family, it is most often due to chance or because family members have been exposed to a common toxin, such as cigarette smoking. Less often, these cancers may be caused by an inherited gene mutation causing a family cancer syndrome. Certain things make it more likely cancers in a family are caused by a family cancer syndrome, such as

• Many cases of an uncommon or rare type of cancer (like kidney cancer).
• Cancers occurring at younger ages than usual (like colon cancer in a 20 year old)
• More than one type of cancer in a single person (like a woman with both breast and ovarian cancer)
• Cancers occurring in both of a pair of organs (both eyes, both kidneys, both breasts)
• More than one childhood cancer in a set of siblings (like sarcoma in both a brother and a sister)
• Cancer occurring in the sex not usually affected (like breast cancer in a man)

Before you decide that cancer runs in your family, first gather some information. For each case of cancer, look at:

• Who is affected? How are we related?
• What type of cancer is it? Is it rare?
• How old was this relative when they were diagnosed?
• Did this person get more than one type of cancer?
• Did they smoke or have other known risk factors?

Cancer in a close relative, like a parent or sibling (brother or sister), is more cause for concern than cancer in a more distant relative. Even if the cancer was from a gene mutation, the chance of it passing on to you gets lower with more distant relatives.

It is also important to look at each side of the family separately. Having 2 relatives with cancer is more concerning if the people are related to each other (meaning that they are both on the same side of the family). For example, if both relatives are your mother's brothers it means more than if one was your father's brother and the other was your mother's brother.

The type of cancer matters, too. More than one case of the same rare cancer is more worrisome than cases of a more common cancer. For some very rare cancers, like cancer of the adrenal cortex, the risk of a certain family cancer syndrome is relatively high with even one case.

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 example, 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.

The age of the person when the cancer was diagnosed is also important. For example, colon cancer is rare in people under 30. Having 2 or more cases in close relatives under 30 could be a sign of an inherited cancer syndrome. On the other hand, prostate cancer is very common in elderly men, so if both your 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.

Certain kinds of benign (not cancer) tumors and medical conditions are sometimes also part of a family cancer syndrome. For example, people with the multiple endocrine neoplasia, type II syndrome (MEN II), have a high risk of a certain kind of thyroid cancer. They also often have hyperparathyroidism (overactive parathyroid glands) and may develop adenomas (benign tumors) of the parathyroid glands and can also can get tumors in the adrenal glands called pheochromocytomas, which are usually benign.

When many relatives have the same type of cancer it is important to notice if the cancer could be related to smoking. For example, lung cancer is commonly caused by smoking, so many cases of lung cancer in a family of heavy smokers is more likely to be due to smoking than to an inherited gene change.

I recognize these and still my cancer snuck up on me!  No wonder there is such hate and dread of the C word, it is the nastiest disease I've ever had to deal with.

Ed