Abstract P6-09-10: Comparison of Age-Specific Patterns of Breast Cancer Risk Factors in a Developing Country

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Abstract Background: Worldwide, breast cancer is the second most common cancer in the world and the most common cancer among women. Although Iran, as a developing country, has had one of the lowest incidence rates of breast cancer among Asian countries, increasing trend of breast cancer incidencerates during last four decades has made it the most frequent cancer among Iranian women. Molecular, epidemiologic and clinical evidences suggest that there are two main breast cancer types. The first breast cancer early onset with peak incidence near age 50 years and the second is late onset with peak incidence near age 70 years. The purpose of this study was to examine the association of established risk factors with breast cancer in women < 50 years and women ≥50 years of age for the first time in Iran, and to ascertain the differences between distribution and strengths of risk factors in these two group of women. Material and Methods: A hospital - based case - control study conducted. Included were 1014 women with histologically confirmed, incident breast cancer and 1014 controls frequency-matched by age and province of residency. All information for the exposures collected during in — person interview or through medical record extraction. Unconditional logistic regression performed to investigate associations of reproductive and anthropometric factors in risk of breast cancer in young and old women. We used Receiver Operating Characteristic (ROC) analysis to compare two models. Results: In the final model in young women, longer lifetime duration of breastfeeding(OR: 0.61; 95%CI: 0.45 — 0.82), positive family history of breast cancer (OR: 1.57; 95%CI: 1.07 — 2.17), employment vs. housekeeping (OR: 1.96; 95%CI: 1.29 — 2.94), ever vs. never oral contraceptive (OC) usage (OR: 1.64; 95%CI: 1.24 — 2.17) and higher parity (OR: 0.46; 95%CI: 0.34 — 0.62) were shown significant association with the risk of breast cancer. In the logistic model for older women, higher education (OR: 1.80; 95%CI: 1.28 — 2.53), employment vs. housekeeping (OR: 2.07; 95%CI: 1.08 — 3.96), later age at first marriage(OR:1.69; 95%CI: 1.19 — 2.40), ever vs. never OC usage (OR: 1.58; 95%CI: 1.17 — 2.13), positive family history of breast cancer (OR: 2.73; 95%CI: 1.79 — 4.18), and BMI ≥30 vs. < 25 (OR: 1.53; 95%CI: 1.06 — 2.23) were shown statistically significant association with risk of breast cancer. The comparison of logistic models demonstrated that age — specific patterns of breast cancer risk factors were different in these two age groups of women(Area Under Curve (AUC) = 0.7442 for women ≥50 years vs. AUC = 0.6635 for women < 50 years; p < 0.001). Conclusion: The trend of increasing rate of employment and education, and decreasing parity and consequently, shorter lifetime duration of breast feeding along with a nation-wide increase in OC usage might be some of the underlying reasons for the rapid rise of breast cancer incidence in Iranian women. Our results showed that these established risk factors can better predict the breast cancer of older women than younger women, so it seems that unknown factors have a greater role in development of breast cancer among younger women. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-09-10.

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