Talking to relatives, it sounds like it was once believed that opening the chest cavity generally caused the spread and growth of diseases such as cancer because of the introduced oxygen into the area.
I couldn't find much information suggesting this, and it sounds like it might be more of an Old Wives' Tale or a remnant myth from the earlier days of medicine. And perhaps it might more have been caused more by lack of sterility and cruder surgical techniques in days gone by.
But I'm interested to know if there's any scientific basis supporting or debunking such an idea.