It depends on the cancer. Some are caused by environmental factors, some by genes.
And sometimes even having the gene for a cancer doesn't mean you'll develop the disease.
Genetic cancer usually requires a trigger of some sort to set it off.
I lost my brother and nephew to cancer, several aunts and uncles. All different types of brain, spinal or bone cancer.
Yet large parts of my family are unaffected.
If you have a family history, you get checked each year by a person with a BACKGROUND in your cancer, not a general practitioner.
And you go on with your life.
Some cancers, like breast cancer, seem to have more of a genetic link.
Talk to your doctor and research that specific cancer that your mother had.