What is sporadic cancer?
Cancer is a common disease. Most of these cancers are considered “sporadic”. Sporadic cancers are isolated occurrences caused by a combination of factors such as the natural processes of aging, environment, and lifestyle. In families with sporadic cancers, the age at diagnosis of cancer is usually later, there are few family members with cancer, and the types of cancer in the family are varied and unrelated. Family members have the same chance of developing cancer as the average person in the general population.
How is hereditary cancer different from sporadic cancer?
A small number of cancers are called “hereditary”, meaning that they are caused by a single major genetic risk factor that is passed down from generation to generation. In families with hereditary cancer, we often see cancers diagnosed at young ages, multiple people with the same or related cancers, and we may even see some people who have developed more than one separate type of cancer. With hereditary cancer, some family members have a much higher chance of developing certain types of cancer than other people. It is important to find families that have a major inherited risk factor, because testing can identify which family members are at higher risk and which are not. This information can then be used to personalize options for early detection or prevention of cancer.
How does hereditary cancer relate to genetics?
When we start life, we inherit two sets of genes – one from our mother and one from our father. A gene is a long stretch of chemical code that our body knows how to read, like letters in an instruction manual. If one or more of the letters in that instruction manual are changed, it is like a spelling mistake, and the body can’t read the instructions anymore. The technical term for this is “pathogenic variant,” (also referred to as a mutation) meaning there is a change to the usual genetic code that stops the body from being able to use the instructions from that gene.
The genes that are involved in hereditary cancer are genes that help control how fast the cells of our body grow. Some of these genes are called “tumor suppressor genes” because they give instructions for repairing damage to our bodies, and they protect us from developing cancer. In families with hereditary cancer, one of these important tumor suppressor genes is not working properly.
Does having a pathogenic variant guarantee cancer?
Having a pathogenic variant does not directly cause cancer, because there is a second copy of the gene from the other parent that is still working properly. However, if we follow people who have one pathogenic variant throughout their lives, we see that they develop more cancers than the average person does because they have less protection against cancer.
If someone has a pathogenic variant, what is the probability of passing that gene to one of their children?
Each child of a parent with a pathogenic variant has a 50% chance of inheriting the gene with the pathogenic variant and a 50% chance of not inheriting the gene with the pathogenic variant. Therefore, even in families with hereditary cancer, about half of the family members do not inherit the pathogenic variant that is causing cancer, and their risk of cancer is similar to the average person. Genetic pathogenic variants do not skip generations and it affects males and females equally.
Is cancer either hereditary or sporadic?
There are also families where the pattern of cancer seems neither sporadic nor clearly hereditary. These families are sometimes described as having “familial cancer,” or a “medium-“ or “moderate-“ risk of cancer. For people in these families the chances of getting cancer are a little higher than the average person. The cause of cancer in these families is “multifactorial,” meaning the cancer is caused by a combination of minor genetic and environmental risk factors.