I saw on ancestry. Com death records for old relatives dating back to 1800.2 of them had cancer! Now I'm worried my family has a cancer syndrome- although most including my direct relatives lived well into their 80's but don't know how they died.

Stop worrying. Back in the old days, most cancers were incurable when discovered, and there was less coronary artery disease. Today one in six people die of cancer; for adults who became parents (your ancestors) in the old days it was probably even higher. This does not make you any different from anyone else. Keep up surveillance and enjoy your life.