A fifth study used blood serum that had been gathered during the late 1960s in a California health maintenance organization 1 to 20 years before cancer diagnosis .
Levels of serum organochlorines were compared among 150 breast cancer cases (onethirdeach Caucasian, African-American and Asian) and an equal number of controls from the same cohort. Although there were
no differences in DDE and PCB levels when the three groups were considered in the aggregate, serum DDE levels appeared
to be as important a risk factor among African-American and Caucasian women
(but not among Asians) as in previous studies (Table 2).