Breast cancer (BC) accounts for 9.1% of all new cancer cases diagnosed in the Republic of Belarus in 2019. This study assessed germinal BRCA1 «founder» mutations frequency and a risk of the disease progression according to BRCA1 status in patients (pts) with different HER2-negative molecular subtypes of BC.
Pts clinical characteristics were collected from N.N. Alexandrov National Cancer Centre of Belarus registry. Ki-67 cut-off was 20%. The main criterias for referring pts with BC for BRCA-testing were young age (<40 yrs) and family history of BC. The statistical differences in genotypes distribution and clinical characteristics among the groups were compared using the chi-square, exact Fisher, Log Rank and U tests.
496 records were provided from January 2018 through September 2022. Median follow up was 19 months; the mean age was 45 yrs.; TNBC – 37,1% (n=184), Luminal B – 30,0% (n=149) and Luminal A – 32,9% (n=163). There was no statistical difference in age and stage distribution between groups with different molecular subtypes of BC. BRCA1 «founder» mutations were detected in 20,4% cases (n=101) with a statistically significant prevalence in TNBC group (TNBC – 35,9%, Luminal B – 20,8%, Luminal A – 2,5%; p<0,001).). BRCA1-mut frequency in pts with early stages of the disease (I-II) was 43,7% in TNBC group and 18,1% in Luminal B (p<0,001). However, pts with advanced stages (III-IV) in both groups have similar frequency of BRCA1-mut (25,9% vs 24,2%). Pts with I-II stages of the disease and BRCA1-mut progressed less frequently during follow up period than BRCA1-WT (Luminal B: 13,3% vs 30,7%, p = 0,17; TNBC: 17,7% vs 36,2%, p<0,05). Pts with III stage of BC had similar tendency in risk of progression depending on BRCA1 status (mut vs WT) in both Luminal B (25,0% vs 45,5%) and TNBC (35,3% vs 48,7%), however non-significant. Also there were no statistical differences in PFS/OS between BRCA1-mut and BRCA1-WT pts with different molecular subtypes of BC.
Germinal BRCA1-mut in pts with Luminal A BC were rare even in selected cohort. BRCA1-mut TNBC more often diagnosed in pts with early stages and had lower risk of progression than BRCA1-WT. In pts with Luminal B HER2- molecular subtype this risk reduction effect was not significant.
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All authors have declared no conflicts of interest.