Human leukocyte antigen as a predictive factor of developing bilateral breast cancer in Japanese women

To investigate the relationship between human leukocyte antigen (HLA) type and bilateral breast cancer, a total of 213 female breast cancer patients were entered into this study. The lymphocyte cytotoxicity test was used for HLA typing. HLA frequency and haplotype antigen frequency were calculated with a microcomputer. A chi-squared test was used for comparing HLA frequency. At the start point of follow-up, 187 patients (87.8%) had unilateral and 26 patients (12.2%) had bilateral breast cancer. After a 10-year follow-up, 183 patients (85.9%) were unilateral and 30 patients (14.1%) were bilateral. Haplotype frequency of A24-Cw7 was significantly higher in bilateral breast cancer patients compared with unilateral breast cancer patients (p < 0.001). After the 10-year follow-up, 4 of 187 patients (2.1%) with unilateral breast cancer developed bilateral breast cancer. Two of 19 patients (10.5%) with haplotype A24-Cw7 developed bilateral breast cancer, whereas only 2 of 168 patients (1.2%) without haplotype A24-Cw7 developed bilateral breast cancer (p < 0.01). The true frequency of developing contralateral breast cancer in patients with haplotype A24-Cw7 was 93 per 100,000 per year. The risk of bilateral breast cancer in patients with haplotype A24 and Cw7 is 12 times higher compared with those without the haplotype. HLA typing is useful for selecting patients who are at high risk of contralateral breast cancer.