Cancer in immigrants as a pointer to the causes of cancer.

The early cancer studies on immigrants, which started to appear some 50 years ago, showed that the incidence in cancers changes to the level of the new host country in one or two generations. These findings were fundamental to the understanding of the environmental etiology of human cancer. Many immigrant groups originate from countries with no cancer registration, and, hence, the immigrant studies may provide estimates on the indigenous cancer rates. The Swedish Family-Cancer Database has been an important source of data for immigrant studies on various diseases. The Database covers the Swedish population of the past 100 years, and it records the country of birth for each subject. A total of 1.79 million individuals were foreign born, Finns and other Scandinavians being the largest immigrant groups. Over the course of years, some 30 publications have appeared relating to cancer in immigrants. In the present article, we will review more recent immigrant studies, mainly among Swedish immigrants, on all cancers and emphasize the differences between ethnic groups. In the second part, we discuss the problem of reliable registration of cancer and compare cancer incidence among non-European immigrants with cancer incidence in countries of origin, as these have now active cancer registries. We discuss the experiences in cancer registration in Morocco and Egypt. We show the usefulness and limitations in predicting cancer incidence in the countries of origin.