As was stated in different words by several of the posters here, this is an epidemiological question.
The question is wether or not non-industrialized nations have cancer.
Fistly, I would like to say that cancer is a not necessarily due to just pollutants, but also to virii, hereditary genetic defects (activated oncogenes), not to mention Uv exposure (sunshine). Papiloma virus alone greatly increases your chances of getting cancer. To presume that a nation would not have cancer because they do not have pollutants is absurd.
Secondly, If one were to compare the tabulated occurances of cancer in the united states, as opposed to some third world country, one may be able to see that the incidence (or prevalence) of cancer in the U.S. is greater than that in the 3rd world country. This is most likely due to under-reporting as hearsurgeon pointed out. If a country is non-industrialized, it is not likely that they have up to date medical facilities able to diagnose cancer, and also it is likely that many people don;t even go to a hospital or see a physician.
In conclusion, what you are asking is answerable by my first point alone. It is probably not very possible to get a good estimate of cancer in a third world country without sending in a epidemiological team with qualified physicians to test samples of the population for a good estimate.
hope that answers your question