BRCA1 and maternal uniparental disomy of chromosome 20: A total of 5925 country-matched female BRCA1 mutation carriers diagnosed with invasive breast cancer were compared with our BRCA1 MBC series, which revealed that MBCs were of significantly higher stage (stage 3–4 vs. stage 1 OR 17.59, 95 % CI 3.47–89.03; P for trend = 0.001) and presented more frequently with lymph node involvement (OR 2.19, 95 % CI 1.03–4.65) than FBCs in BRCA1 mutation carriers (Additional file 5).