What is true about smoking scientist knew in 1940 that it causes cancerlung cancer rates rise and fall or lung caner was common in 1920?

Answer 1

In the 1920s and 1940s scientists did not know nor did they have any idea what caused cancer. In the 1930s the sulfa drugs gave doctors the ability to fight infections. Penicillin became available after World War 2. Also after world war 2, people replaced coal with natural gas for home heating. At that point it became possible to test the effect of cigarette smoking because coal smoke no longer filled the air.

It was possible to take the members of a Seventh Day Adventist Church, where none of the members smoked, and compare them to the members of a Baptist Church where many members smoked. The members came from the same socioeconomic level. Without the houses filled with coal smoke, the smoke in the lungs probably came from cigarette smoke. Since neither the Adventists nor the Baptists were supposed to drink alcohol, that could be ruled out.

So, basically it was almost 1950 before serious research on smoking became possible. It was the early 1960s with the report was released linking smoking and cancer.