In addition to BRCA1 and BRCA2, RAD51C,PALB2 and BRIP1 are known as breast cancer susceptibility genes. However, the mutation status of these genes in Japanese familial breast cancer cases has not yet been evaluated. To this end, we analyzed the exon sequence and genomic rearrangement of RAD51C,PALB2 and BRIP1 in 100 Japanese patients diagnosed with familial breast and ovarian cancer and without BRCA1 and BRCA2 mutations. We detected a large deletion from exons 6 to 9 in RAD51C, 4 novel BRIP1 missense variants containing 3 novel non‐synonymous variants, c.89A>C, c.736A>G and c.2131A>G, and a splice donor site variant c.918+2T>C. No deleterious variant of PALB2 was detected. The results of pedigree analysis showed that the proband with a large deletion on RAD51C had a family history of both breast and ovarian cancer, and the families of probands with novel BRIP1 missense variants included a male patient with breast cancer or many patients with breast cancer within the second‐degree relatives. We showed that the mutation frequency of RAD51C in Japanese familial breast cancer cases was similar to that in Western countries and that the prevalence of deleterious mutation of PALB2 was possibly lower. Furthermore, our results suggested that BRIP1 mutation frequency in Japan might differ from that in Western countries.

The long-term prognoses of patients for whom dissection was omitted owing to negative sentinel lymph node metastases were similar to those reported previously-low recurrence and mortality rates. The frequency of axillary lymph node recurrence and the post-recurrence outcome differed between luminal and TN cases, with recurrence being more frequent in patients with the TN subtype. TN patients also had poorer prognoses, even after receiving additional dissection and anticancer agents after recurrence.

Individuals carrying pathogenic BRCA1 or BRCA2 mutations have an increased lifetime risk of breast and/or ovarian cancer. The incidence of breast cancer amongst disease-free BRCA mutation carriers under surveillance and the clinical and pathological characteristics of those who subsequently develop the disease remain unclear in Japan. We reviewed the records of 155 individuals with BRCA1 or BRCA2 mutations identified by genetic testing between January 2000 and December 2016. At the time of genetic testing, 26 individuals with one of these mutations had no history of breast cancer and were therefore enrolled in a surveillance program that included biannual ultrasonography, clinical breast examination, annual mammography, and conditional magnetic resonance imaging for the early detection of primary breast cancer. During the surveillance period, 5 individuals with BRCA1 or BRCA2 mutations were diagnosed with primary breast cancer. The mean surveillance duration until breast cancer diagnosis was 48 months. The incidence of primary breast cancer during surveillance in initially disease-free BRCA mutation carriers was 4.23%/year. In two cases, the tumors were only detectable on MRI. The case 5 patient who presented with a tumor that was detected by self-examination, which then grew rapidly, had stage IIB triple-negative breast cancer. In conclusion, our results show that some challenges exist in the early detection of breast cancers in BRCA1 or BRCA2 mutation carriers. There are also some difficulties in approaching those individuals in Japanese society.

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