Abstract

Breast density has been shown to be a strong risk factor for breast cancer, whereby women with mostly dense breasts have approximately four times the risk of breast cancer than women of the same age and weight with mostly fatty breasts. Mammographic density is also associated with classical reproductive risk factors: it is lower in women who have had children and who have breast fed them. Breast density varies greatly by age and weight: dense breasts are more common in young and women who are not overweight.
This study aimed to assess the relationship between density and risk of breast cancer in this case-control study from the IBIS-I trial from thirty-six centres in nine countries.
This was a randomized controlled trial designed by the International Breast Cancer Intervention Study. Women with available Mammogram result after their first follow-up were used. Cases were women who developed breast cancer and controls were still free (Outcome). Other variable are age (years), body mass index (BMI), and treatment arm (placebo, Tamoxifen). The relationship between breast density and risk factors was assessed by correlation, independent T-test and multiple logistic regression.
A total of 1065 women were analyzed. The women that developed breast cancer after their first follow-up mammogram was 11.5% (n=123). Their mean age was 50.2±6.2 years. There was a significant relation between breast density and the outcome (T-test value=2.380, CI of 95%: -12.5, -1.2). Breast density and age (r=-0.232, P-value=0.0001) and BMI (r=-0.0.415, P-value=0.0001) were correlated. There was a weaker risk factor after adjustment for age and BMI, though not significant different (unadjusted odds ratio= 1.008 and adjusted odds ratio= 1.006). Increase in risk of breast cancer was associated with aging and increase in BMI. Meanwhile, decrease breast density was related with increase in age and BMI, this inverse relationship could reduce effect of breast density on breast cancer.
The significant of relation between breast density and the outcome is an indication that breast density is a risk factor for breast cancer in this case-control study. The relationship that exists between breast density and the two risk factors are in opposite direction. It is important for women know there breast density to detect or prevent breast cancer early.