Prevalence and differentiation of hereditary breast and ovarian cancers in Japan.

Background: We assembled needed data on the prevalence and characteristics of BRCA1/2 in Japan.

Materials And Methods: Our study of BRCA1/2 collected data at eight institutions in Japan on 320 individuals with a strong family history of breast cancer, according to the NCCN guidelines, by the end of March 2012.

Results: Among 260 proband cases, 46 (17.7 %) were positive for BRCA1, and 35 (13.5 %) were BRCA2-positive. Therefore, the total pathological mutation rate was 30.7 %. Pathology data after breast surgery were obtained from 37 cases of BRCA1 mutation, 23 (62.2 %) of which were triple negative (TN). On the other hand, 29 cases (82.9 %) of BRCA2 mutations were Luminal type. The most prevalent BRCA1 mutation site was L63X, found in 10 families. L63X was reported previously by studies in Japan, and it may be a founder mutation. We found two cases of large deletion detected by multiplex ligation-dependent probe amplification. One was an entire deletion of exon 20 and the lacked exons 1-9. TN with a family history of ovarian cancer was 11/20 (55 %). TN under 40-year-old (y.o.) 15/23 (65.2 %) and TN with one or more breast cancers in family history 17/32 (53.1 %) showed higher incidences of BRCA1 mutation.

Conclusion: Hereditary breast and ovarian cancer (HBOC) may have nearly the same prevalence in Japan as in the US or Europe. If TN cases are taken into account, the ratio of BRCA1 is higher. L63X may be one of the founder mutations in Japan. A nationwide database of HBOC is important to develop risk models for BRCA1/2 carriers in Japan.