[removed]

"Cancer" is a large set of diseases, some of which are caused partly or entirely by inherited genes and some of which are not. Few cancers are caused entirely by inherited characteristics. Instead, some genes make it more likely that a person will develop a particular form of cancer but there is usually some environmental condition that also causes actual cancer to develop.

This can, for example, be that a person has a gene that makes some cells more likely to divide and multiply out of control than usual, but their general immune system cancer-suppression works OK and suppresses it until they have a degraded immune system for another reason. Then they develop cancer.

Or a person may be more prone to cancer, and are then exposed to a further environmental carcinogen, and they develop cancer. Another person with the same predisposition who is not exposed, may not develop cancer.

Even without any predisposition towards being more likely to develop cancers (which is very unlikely - no-one has a perfect genome), exposure to a strong carcinogen may still cause you to develop cancer.

There are also many random factors, such as cosmic rays (literally), that can cause cancer to begin in some part of your body. It's not very likely, but it's definitely possible.

If you don't have any known predisposition towards cancer, then it's probably not something to worry about.

Avoid risk factors like smoking, get your colon checked when you're 50, check your breasts and/or testicles for lumps on a regular basis, and get any odd lumps or persistent unexplained pains, changes in appetite or weight, etc, checked out, but don't go around worrying every day.

Thanks for this!

All cancer is genetic but not all cancer is hereditary. Essentially all cancer comes from DNA damage which changes the cell to become cancerous.

Many environmental exposures can cause this, and for some individuals they are born with a genetic trait which makes them more susceptible to cancer. At the end of the day even the healthiest person in the world has a chance of cancer and many risk factors are outside of our control. For example all women have a higher risk for breast cancer (~11%) simply because they have more breast tissue than men. Then your risk is further influenced by other things like age of menstrual period, if you ever gave birth, if you have naturally dense or fibrous breasts, etc etc.

Like the other commenter said, if you have no family history that’s definitely a good thing, but nobody has “nothing to worry about” when it comes to cancer. That’s why regardless of family history or lifestyle, If you’re a woman you need to get annual breast exams when you reach a certain age, all men need prostate screening eventually, and everyone needs a colonoscopy eventually. These are all screenings for common cancers which can occur in anyone.

[removed]

While this is a very good answer I would not agree with:

>If you don't have any known predisposition towards cancer, then it's probably not something to worry about.

There are certainly things that massively increase your relative risk of cancer even if you don't have a genetic predisposition. I know you already said that exposure to strong carcinogens may cause you to develop cancer, and this may be talking about specifically things like cosmic rays, but the context of this sentence as a stand alone paragraph in your answer makes it sound like a more broad statement.

Smoking is definitely something that will significantly increase your risk of cancer even without a genetic predisposition to an extent that it's entirely appropriate to worry about it. If you have a genetic predisposition it's worse but it's still worrisome without one. There are others too but this is a big one in terms of common lifestyle factors.

[removed]