Even for cancers for which there is statistically significant evidence of heritable component most pairs of twins were discordant for the cancer - indicating that, on the population level the increase in risk of cancer even among close relatives of affected persons is generally moderate. The answers seems to be that genetics is important, but unusually is it a great factor in the majority of cancers. For those who suffer a familial trait that is adverse, this news is of little comfort. Certainly, work is underway to diminish genetic influence. For breast cancer family members, medicines like Tamoxifen can decrease the risk of invasive malignancies.
Early detection is frequently important.
For prostate detection, early diagnosis means the highest cure rates. For this, physical exams, blood testing of PSA or prostatic specific antigens and often ultrasounds or biopsies are crucial. Cessation of smoking and routine high resolution CT scanning should simultaneously decrease the incidence of lung cancers and increase early detection hopefully also saving lives. It is the sign of intelligence that we do. As it is said, those who do not learn from history are condemned to repeat it.