For example, if someone discovers they have breast cancer or cancer in the liver or something, does that mean that they always had cancer but it was not able to be detected until they discovered they had it? Or is that something that is formed later, and wasn’t always in that person’s body?
In: Biology
Cancer happens when your cells divide at a rate that isn’t normal for them.
Typically cells divide in an orderly process–everything needs to be in place before the cell decides to divide. Your skin cells are a good example of this–they’re constantly dividing and you’re always sloughing (gross verb, sorry) dead skin cells here and there.
Cancer happens when the genes that control that process get messed up. For example, we have genes that act as the brakes in this process–they tell the cell “Do not divide, do not divide, until I tell you to divide.” We have two copies of those kinds of genes–we inherit one copy from one parent, and the other copy from the other parent.
Say you get a bad sunburn, and the UV radiation causes the DNA for one of those genes to get damaged in one of your skin cells. That skin cell keeps dividing normally, but now it only has *one* copy of that gene protecting it from becoming cancerous.
Say you get another bad sunburn, and the *other* copy of that gene gets damaged as well. Now you have *zero* copies of that gene to put their feet on the brakes, and that cell can divide as much as it wants. This is what causes cancer. This is what we call the “two-hit hypothesis.”
80-90% of the time, cancer is what we call *sporadic*. This means those cancers are caused by these genetic mutations our cells *acquire* or *accumulate* over time, with age being the biggest risk factor–the more years you have under your belt, the more opportunities for your cells to acquire those changes and cause cancer. Because of this, if you have lots of members of your family living into old age, it’s not uncommon to see sporadic cancers here and there.
About 5-10% of the time, however, cancer is caused when a person *inherits* a non-functional gene from a parent that *should* be putting its feet on the brakes, but in actuality isn’t showing up to work in the morning. These people often develop cancer at younger ages, because they only need *one* acquired genetic mutation (such as through a bad sunburn) for that cell to become cancerous. These cancers are what we would call *hereditary*.
Edit: If you have a family history of young cancers, such as breast, colon, or uterine cancer under the age of 50, you could be at a higher risk of carrying a gene that increases your lifetime risk of cancer. A genetic counselor can help you talk through your family history, what your risk may be based on family history, and the benefits and limitations of genetic testing in learning more information. The National Society of Genetic Counselors (NSGC) has a [directory](https://findageneticcounselor.nsgc.org/?reload=timezone) if anyone is interested in learning more about their cancer risk, and the ways that we can manage or even reduce that risk.
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