The risk factors and prognosis of bilateral primary breast cancer: a comparative study with unilateral breast cancer.

This study was performed to determine the risk factors and evaluate the outcome of bilateral breast cancer (BBC). We reviewed the records of 170 patients with BBC and 1,677 with unilateral breast cancer (UBC), and compared their personal history, histopatholgical characteristics, clinical findings, and treatment, and postoperative follow-up records. The patients with UBC were more likely to develop contralateral cancer with the features including: young age at onset, especially younger than 40, premenopause, late primiparity, breast cancer family history, benign mammary disease history, and a tumor larger than 5 cm (p < 0.05). After adjustment by multivariate analysis, we concluded that breast cancer family history and age at onset younger than 40 years old were the independent risk factors for BBC. There were no significant differences for distant metastasis or overall survival between BBC and UBC (p > 0.05). We observed that 64.1% of the second breast cancer occurred within 5 years after the operation of the first cancer, and medical examination could improve the early diagnosis of the contralateral breast cancer. Contrary to common belief, our study showed that BBC and UBC had similar biological features and prognosis (p > 0.05). The excessive treatment and prophylactic measures may be unnecessary in this seemingly aggressive breast cancer. The patients with UBC younger than 40 or with breast cancer family history should have intensive contralateral breast followup, especially within 5 years after in the initial treatment.