Incidence pattern and spatial analysis of breast cancer in Iranian women: Geographical Information System applications.

Background: Breast cancer is the leading cancer in Iranian women, but no studies have yet been conducted on the distribution and pattern of its incidence.

Aim: To perform a spatial analysis and determine the incidence pattern of breast cancer in the Islamic Republic of Iran.

Methods: This was a cross-sectional, pathology-based study of all new female patients with breast cancer registered in the Islamic Republic of Iran in 2011 (n=10 233). Initially, crude incidence rates were calculated for each province and the whole country per 100 000 person-years. Then, a direct standardization method and World Health Organization standard population were used to adjust for age effects on a geographical scale. Stata and Arc GIS software were used to calculate incidence rates and conduct spatial analysis.

Results: The mean (standard deviation) age of the patients was 50.9 (12.6) years. The national age-standardized incidence rate for breast cancer in women was 29.88 per 100 000 person-years, with a range of 5-72 in different provinces. The clustering incidence pattern was observed in Mazandaran, Tehran, Alborz, Isfahan and Markazi Provinces (P < 0.01). There was a significant cluster of high incidence of breast cancer in Iranian women.

Conclusion: These findings may help to establish etiological hypotheses of cancer causation and identify spatial anomalies in cancer incidence or registration in the Islamic Republic of Iran. Our findings may also aid further research on the possible explanations for these clusters and associations.