The longer the exposure the more likely they were to get cancer. There is a time lag between the start of the exposure to a carcinogen and the time a person gets cancer. Age at which a woman has first child is correlated with breast cancer. Person who has no children has an incidence equal to person whose first child is born when they are 35. Person whose first child is born after age 35 has a risk of cancer greater than for women who have never had a child.
Environmental cancer is potentially preventable.
One piece of evidence is where in the body cancer is most frequently seen. Tissues exposed to the environment are external surfaces and internal surfaces in contact with things we breathe or eat. Another piece of evidence comes from comparing the incidence of cancer in different countries. Here are some examples of countries with different incidence of different types of cancer for men. Stomach cancer high in Japan and low in United States.