Determining Breast Cancer Risk Factors

Medical researches attempt to define risk factors in order to discover who is most likely to get a particular disease and also to find clues as to the disease's cause and thus to the prevention and cure.
A risk factor is usually determined by taking a large population of people - say 1,000-2,000 or more - and identifying a variety of features about them, determining who gets the disease under study and then seeing what the relationship is between the disease and the features that commonly occur within the group. It is important how the findings from population researches are being used. If you determine that out of your 2,000 people under study, 500 got the disease and all 500 drank milk as infants, you can't decide from this that milk-drinking causes breast cancer. If none of the 1,500 drank milk as infants, you might be on the right track; if; as is more likely, all 1,500 did drink milk, you've learned nothing except that most people drink milk as children.
Sometimes, as in the case of lung cancer and smoking, risk factors are dramatic and can make a clear difference to the individual's likelihood of getting the disease. Unfortunately, it usually doesn't work this way. In breast cancer, several risk factors, such as family history, have been identified. But so far, there is nothing comparable to the correlations found between cholesterol and heart disease, or between cigarette smoking and lung cancer. 70% of breast cancer patients have none of the classical risk factors in their background. It is important to understand this for two reasons. Overestimating the importance of risk factors can cause needless mental distress if you have one of them in your background. On the other hand, you may create a false sense of security if you don't have them. Most breast cancer patients do not have a family history of breast cancer. By virtue of being a woman, you are at risk of breast cancer.
Another thing to note is that the risk factors do not necessarily increase in a simple arithmetical fashion; if one risk factor gives you a 20% risk of acquiring breast cancer and another gives you another 10% chance, it doesn't always mean that you're up to 30%. The interaction of risk factors is a tricky and complicated process. One interesting example is in the studies on alcohol and breast cancer, which shows that women with other risk factors who also drank liquor didn't increase their risk very much, while women with no other risk factors who drank raised their risk dramatically.
Most breast cancer still occurs in white women over 50 - about 50% of cases. Your risk at age 30 is 1 in 5,900 / year. By age 40, it is 1 in 1,200 / year, so the risk of getting breast cancer before you're 50 is very small. The median age of diagnosis of breast cancer is 64, which means that half of women who get breast cancer will get it before age 64 and half will get it after. So whenever risk factors or breast cancer is discussed, it is important to correct for age. Other risk factors - family history, hormonal factors, etc. - will most likely cause breast cancer only in combination with rising age.
Another factor that needs to be considered is the effect of variability of ethnic groups. The risk of African-American women and other women of color is less than that compared to Caucasian women. This is a disease that is predominantly found in non-Hispanic white women. African-American women have rates similar to those of white women premenopausally. That won't necessarily be comforting news to African-American women, however, though it's less common in that group, it's often more deadly.
The difference in vulnerability to breast cancer works on international level as well. Third world countries have less breast cancer than highly industrialized countries.