RESUMO
BACKGROUND: Cancer is a complex disease caused by multiple factors, both genetic and environmental. It is a major health concern worldwide, in the Middle East and in Jordan specifically and the fourth most common killer in the Middle East. HYPOTHESIS: The relative genetic homogeneity of the Circassian and Chechan populations in Jordan results in incidences of cancer that differ from the general Jordanian population, who are mostly Arabs. MATERIALS AND METHODS: National Cancer Registry data were obtained for the years 1996-2005 The Chechen and Circassian cancer cases were identified and cancer registry data were divided into three populations. Crude rates were calculated based on the number of cancer cases and estimated populations. RESULTS: Breast cancer is the most common cancer type constituting about one third of female cancers in all three populations. Higher crude rates are observed in the Circassian and Chechen populations than in the Arab Jordanian population. The rate ratios (95%CI) in Circassians and Chechens with respect to the Arab Jordanian population are 2.1 (1.48, 2.72) and 1.81 (1.16, 2.85), respectively. Lung cancer is the most common cancer in male Arab Jordanians and Chechens with crude rates of 4.2 and 8.0 per 100,000 respectively. The male to female ratio in these two populations in respective order are 5:1 and 7:1. The lung cancer crude rate in Circassians is 6.5 per 100,000 with a male to female ratio of only 1.6:1. The colorectal cancer crude rates in Arab Jordanians and Chechens are similar at 6.2 and 6.0 per 100,000, respectively, while that in Circassians is twice as high. CONCLUSIONS: Considerable ethnic variation exists for cancer incidence rates in Jordan. The included inbred and selected populations offer an ideal situation for investigating genetic factors involved in various cancer types.