Urban-rural differences in breast cancer incidence by hormone receptor status across 6 years in Egypt

Abstract

Breast cancer incidence is higher in developed countries with higher rates of estrogen receptor positive (ER+) tumors. ER+ tumors are caused by estrogenic exposures although known exposures explain approximately 50% of breast cancer risk. Unknown risk factors causing high breast cancer incidence exist that are estrogenic and development-related. Xenoestrogens are such risk factors but are difficult to study since developed countries lack unexposed populations. Developing countries have urban-rural populations with differential exposure to xenoestrogens. This study assessed urban-rural breast cancer incidence classified by hormone receptor status using data from Gharbiah population-based cancer registry in Egypt from 2001 to 2006. Urban ER+ incidence rate (per 100,000 women) was 2-4 times (IRR = 3.36, 95% CI = 4.84, 2.34) higher than rural incidence rate. ER-incidence rate was 2-3 times (IRR = 1.86, 95% CI = 2.38, 1.45) higher in urban areas than in rural areas. Our findings indicate that urban women may probably have a higher exposure to xenoestrogens.

Figure 1

Age-specific urban-rural incidence of breast cancer by hormone receptor status in Gharbiah, 2001-2006. All incidences are per 100,000 women. There are 6 age-groups: 0-29, 30-39, 40-49, 50-59, 60-69 and 70 or more, each represented by a point on the graph for each year in that sequence.

Figure 2

Age-specific urban-rural incidence of breast cancer by joint hormone receptor status in Gharbiah, 2001-2006. All incidences are per 100,000 women. There are 6 age-groups: 0-29, 30-39, 40-49, 50-59, 60-69 and 70 or more, each represented by a point on the graph for each year in that sequence. ER+/PR− and ER−/PR+ categories had very few cases and were excluded from this graph.