Background: High socioeconomic status and migration to a higher risk area have been linked to increased breast cancer risk. To evaluate the occurrence of breast cancer in women of different social class and residential history, we conducted a multicentre case-control study in Italy.
Methods: A total of 2569 cases of incident breast cancer were ascertained in northern, central and southern Italy. The controls were 2588 women admitted for a wide spectrum of acute conditions to the same hospitals where cases had been hospitalized. The effect of socioeconomic variables was evaluated with multiple logistic regression after stratification and adjustment for age, origin, centre, and selected reproductive and dietary factors.
Results: Compared to housewives, managers and professionals had a 1.7-fold increased risk, whereas the relative risk was 0.7 and 0.6 respectively in helpers and manual workers. The risk of breast cancer also increased with increasing social level of the husbands's occupation and subjects's number of years of schooling. Women who originated in central and southern Italy, and migrated to northern Italy after age 24, but not those who migrated at a younger age, had a relative risk of 0.6 and 0.7 respectively, compared to lifelong residents in northern Italy.
Conclusions: Our findings show that correlates of sociocultural level and place of origin exert an influence on breast cancer risk which is not accounted for completely by known risk factors (i.e. reproductive and menstrual characteristics and recent dietary habits). Such influence may thus occur early in life.