Follow-up of tissue genomics in BRCA1/2 carriers who underwent prophylactic surgeries

Purpose The genomic status of non-malignant tissues from carriers of pathogenic germline BRCA1/2 (g BRCA1/2 ) variants may reveal information towards individualized prophylaxis. We performed spatiotemporal tissue genotype comparisons in a real-life cohort of g BRCA1/2 carriers of Greek origin, who underwent multiple risk-reducing/prophylactic surgeries at various time points. Methods Fifty-three women (median age 36 years) within cancer families were observed for up to 37.5 years; 43 were cancer carriers and 10 were healthy carriers. Histology review and genotyping were performed for 187 paraffin tissues (average: 3.5 per carrier) including 46 carcinomas (40 breast) and 141 non-malignant breast and gynecological samples. Results High allelic imbalance (AI) and somatic pathogenic TP53 variants were present in cancer carriers only ( p values < 0.0001). High AI was associated with g BRCA1/ 2 indels ( p < 0.0001) and g BRCA2 alterations ( p = 0.0109). Somatic (pathogenic) variants were infrequently shared between non-malignant tissues and matched carcinomas. Aberrations of g BRCA1 variant heterozygosity were noticed in tissues from cancer carriers only (13/43, 30.2%). These pertained to classic LOH (neoplastic lesions in 9/43 carriers, 20.9%) and under-representation of the germline variants (5 samples, 4 non-malignant, all in the breast). Both aberrations coexisted in matched samples in one case. Over time, germline variant heterozygosity prevailed in non-malignant tissues; intra-carrier genomic alterations were aggravated (21.1%), ameliorated (26.3%) or remained stable. Conclusion This real-life case study supports the need to address tissue genotypes from prophylactic surgeries in combination with polygenic scores towards personalized prophylaxis. To this end, knowing the traditionally classified pathogenic potential of a g BRCA1/2 variant may not be enough.