RISK-FACTORS FOR CONTRALATERAL BREAST-CANCER IN CHENNAI (MADRAS), INDIA

Background This is the first cohort study conducted in India to identi fy risk factors for contralateral breast cancer (CBC) among patients w ith first primary breast cancer. Methods Patients with first primary b reast cancer diagnosed in 1960-1989 at the Cancer Institute (WIA) in C hennai, India, were followed-up until 31 December 1994. The risk of CB C was assessed among unilateral breast cancer (UBC) patients who survi ved for >12 months following the diagnosis of breast cancer and did no t develop a second cancer (n = 2665) and among those who developed a C BC greater than or equal to 12 months after the diagnosis of breast ca ncer (n = 39). Results The age-adjusted incidence of CBC among women w ith UBC was seven times the incidence (per single breast) in the gener al population. Among women with UBC the relative risk (RR) was 4.5 (95 % CI:1.1-19.6) comparing those with and without a history of breast ca ncer in the mother, and 2.8 (95% CI : 1.2-6.7) comparing age at first birth 21-25 versus earlier. The RR was 0.3 (95% CI: 0.1-0.6) comparing those with and without hormone therapy for their UBC. Radiotherapy fo r the UBC had no significant effect on the incidence of CBC. Conclusio n Positive family history of breast cancer and later age at first chil dbirth emerged as stronger risk factors for CBC than UBC. Hormone ther apy reduces the risk of CBC.