A case-control study on breast cancer risk factors in a southern European population.

A case-control study has been carried out among women attending a screening service in Palermo (Sicily) from 1974 through 1983 to ascertain the distribution of the most frequently investigated risk factors for breast cancer in a southern European population. Information has been obtained from the archives of the screening service. The analysis was separately conducted for pre- and post-menopausal cases and non-cases. Risk factors for pre-menopausal women are: nulliparity (nulliparous versus parous: OR 2.17, 95% CI 1.41-3.32); age at first birth (25-29 versus less than 20: OR 2.16, 95% CI 1.17-4.00); interval between menarche and first birth (greater than 20 years versus less than 6: OR 5.34, 95% CI 2.08-13.66); number of births (greater than 4 versus 1-2: OR 1.98, 95% CI 1.10-3.50). Risk factors for post-menopausal women are: nulliparity (nulliparous versus parous: OR 2.18, 95% CI 1.59-2.99); age at first birth (greater than 29 versus less than 20: OR 1.84, 95% CI 1.13-2.99); interval between menarche and first birth (16-20 years versus less than 6: OR 2.15, 95% CI 1.20-3.85). Age at menarche, age at menopause, breast feeding and family history were not found to be risk factors for breast cancer in the investigated population. The existence of influencing differences between northern and southern populations has been postulated.