How can genetic tests predict cancer?

Like forecast : Genetic test will predict potential to develop cancers , by certain signs. Certain cancers are genetically transmitted , they lack the protective mechanisms to repair damaged cell & allows them to become cancer cells , like braca i& ii . In breast cancer, cognitional colon polyps, lynch syndrome etc could be tested in affected family members if positive could treat successfully in early stage.

Some predict risk: Some genetic tests diagnose cancer, others, like BRAC1 and 2, predict increased risk if a person has a pathologic genetic variant. For example, a specific BRCA 2 variant may change the risk of a woman developing ovarian cancer from around 1 in 70, almost always postmenopausal, to 1 in 2 by age 50; women informed of this increased risk may choose prophylactic oophorectomy, like Angelina Jolie.