If the cancer is caused by overuse of alcohol or by smoking / other tobacco use, it can certainly be prevented. Most cases of lung cancer originate from tobacco use and so are preventable.
There are other factors that can cause cancer. Some of them include lack of exercise, obesity and poor nutrition. Obviously, these types of cancers can be prevented with the right lifestyle changes. At the very least, the chances of getting cancer from these causative factors can be minimized.
Prolonged exposure to the sun’s ultraviolet rays can contribute to skin cancer. The incidence of this type of cancer could be significantly reduced by regulating exposure to the sun and also by avoiding practices like indoor tanning.
So yes, certain types of cancers can be prevented.