EPIDEMIOLOGY OF IN-SITU AND INVASIVE BREAST-CANCER IN WOMEN AGED UNDER 45

The incidence of in situ breast cancer in the USA has increased rapidl y in recent years, even among young women. A population-based case-con trol study of 1616 breast cancer cases aged under 45 in the USA was us ed to examine risk factors for in situ, local and regional distant tum ours. Almost 60% of in situ tumours were detected by routine mammogram s compared with 18% of local rumours and 8% of regional/distant tumour s. After adjustment for screening history and established risk factors , family history of breast cancer in a first-degree relative and Afric an-American race were associated with an increased risk of all stages of breast cancer. The associations with nulliparity. a previous breast biopsy and body mass index were significantly stronger for in situ tu mours than for local or regional distant disease. Alcohol consumption was associated with an increasing trend in risk of regional distant ru mours but not of earlier stage rumours, indicating that alcohol may be involved in late-stage events. Analyses by histological type of in si tu tumours suggested that both ductal and lobular carcinoma in situ we re associated with most established breast cancer risk factors, and th e magnitude of association tended to be greater for the ductal form.