BACKGROUND: The causes and pathologic and prognostic phenotypes of late-onsetfamilial breast cancers are still unknown. The purpose of this study was to document the clinicopathological features of late-onset familial breast cancers using genetic testing of BRCA1 and BRCA2. METHODS: We analyzed 11 breast cancers from 10 patients from 8 Japanese late-onset Breast cancer families. RESULTS: The average age of the patients was 55 years (range 43 to 89). Bilateral occurrence was noted in 2 patients (8%). All the tumors were invasive ductal carcinomas, except for 1 case of invasive lobular carcinoma. Tumor size rangedfrom 0.8 cm to 7.8 cm (median 2.3 cm) and lymph node metastasis occurred in 6 of the 11 patients (55%). Six (55%) of the 11 tumors were histologically grade 2 and 5 (45%) were histologically grade 3. Estrogen receptor (ER) positivity was 80% (8/10). Overexpression of c-erbB-2 and p53 protein was detected in 18% (2/11)and 9% (1/11) of the tumors, respectively. Five patients from 4 families received genetic testing but all were negative for BRCA1 and BRCA2 germline mutations.All the patients were alive after a median follow-up period of 32 months, except for 1 patient. CONCLUSION: In this study, no germline mutations of BRCA1 or BRCA2 were detected. However, there was a tendency towards ER-positive tumors, but the positivity of p53 protein was considered to be lower then that of sporadic tumors.