The development of a homologous recombination deficiency (HRD) score to identify HR-deficient tumors.

Abstract

e18085 Background: BRCA1/2 mutated cancers are homologous recombination repair (HRR) deficient and often sensitive to drugs targeting DNA repair pathway. Emerging evidences suggest tumors with mutations in other HRR genes might also respond favorably to DNA repair pathway targeted drugs; however, the results were inconclusive. Genomic instability is characterized by telomeric allelic imbalance (TAI), large-scale transition (LST) and loss of heterozygosity (LOH). Here, we developed an HRD score based on assessing the status of these patterns in tumors. Methods: 73 cancer patients, including 36 breast cancer (BC), 35 ovarian cancer (OC) and 2 prostate cancer (PC) patients were recruited. 28 were BRCA-deficient tumors (10 BCs, 17OCs and 1 PC) harboring pathogenic/likely pathogenic (P/LP) germline mutation in BRCA1/2 with LOH. 13 BRCA-mutated tumors (10 BCs, 2 OCs and 1 PC) carried P/LP BRCA1/2 mutation without LOH. The rest 33 were HRR wild type controls (16 BCs and 16 OCs). All samples were profiled using a panel consisting of 24 classic HRR genes and their adjacent SNPs. The scores for TAI, LST and LOH were developed separately and an incorporated HRD score based on the 3 patterns was established. Clinical data of 42 OC pts were collected to validate the algorithm. Results: All pairwise correlations of TAI, LST and LOH scores showed high correlations (TAI vs. LOH: r = 0.89; TAI vs. LST: r = 0.92; LST vs. LOH: r = 0.83). The univariate logistic regression was used to assess the correlation of the score with BRCA deficiency. In the cohort of BRCA-deficient vs. HRR-negative, the scores of TAI (P = 9.72 x 10−4), LST (P = 8.75 x 10−5), LOH (P = 0.01) and HRD (P = 3.35 x 10−4) all showed significant associations with BRCA-deficiency. In the cohort of BRCA-deficient vs. BRCA-mutated +HRR-negative, all the scores also highly correlated with BRCA-deficiency (TAI: P = 2.35 x 10−4, LST: P = 1.48 x 10−5; LOH: P = 2.36 x 10−4, HRD: P = 6.29 x 10−5). Using 42 as a cutoff, it achieved sensitivities of 94.1%, 60% and 82% for identifying BRCA-deficient tumors in the 35 OCs, 36 BCs and in all 73 tumors, respectively. We further validated the predictive value of HRD score in an additional 42 OC pts and found significantly higher HRD sore in pts sensitive to platinum therapy (P = 0.036). Patients having an HRD score > 42 had a significantly longer PFS than pts with a score < 42 (p = 0.04). Conclusions: Our study developed a HRD score base on assessing 3 patterns of genomic instability (TAI, LST and LOH). The HRD score revealed a promising value in detecting HR-deficient tumors (especially BRCA-deficient).