Beyond BRCA? clinical utility of homologous recombination deficiency in gastrointestinal cancers.

Abstract

472 Background: There is emerging evidence about the predictive role of homologous recombination deficiency (HRD) in multiple cancers. The clinical utility of HRD is less well defined in gastrointestinal (GI) malignancies. Methods: We reviewed the whole genome (WGS) and transcriptomic (RNA-Seq) data of patients with advanced GI cancers between 2012-2018 in the Personalized Oncogenomics trial (NCT02155621). Scores were calculated as the sum of loss of heterozygosity, telomeric allelic imbalance, and large-scale state transitions scores. HRD was defined as a score ≥34. Mutational analysis was performed to determine the presence of mutational signature 3, which is usually strongly associated with BRCA status. Retrospective chart review was conducted to extract treatment and survival outcomes. Overall survival (OS) from initiation of first-line systemic therapy and time to progression on platinum therapy (TTPp) were calculated. Linear and multivariable regression analyses were conducted. Results: Of 154 patients with GI primaries, 56% were male and 105 (68%) were exposed to a platinum agent in the metastatic setting. Primary sites included upper GI (N=20, 9%), pancreas (N=35, 16%), colorectal (N=74, 33%), and other GI primary (N=25, 11%). Ten patients (6%) had a BRCA1/2 mutation, 20 (13%) had a high HRD score, and 11 (7%) had a high signature 3 score (>0.05). Six patients had both high HRD and high signature 3 scores (Table). On linear regression, high HRD scores and mutational signature 3 were independently associated with longer TTPp (β=4.17, 95% CI 0.15-8.19, p=0.04; β=8.03, 95% CI 2.87-13.18, p<0.05, respectively). On multivariable linear regression, after adjusting for HRD score, BRCA1/2 status, and tumor site, only cases with a mutational signature 3 retained significance ( p<0.05). HRD status was not prognostic for OS (HR 1.02, 95% CI 0.65-1.62, p=0.92). Conclusions: Within a cohort of patients with GI malignancies characterized by WGS and RNA-Seq, mutational signature 3 was more strongly associated with TTPp compared to HRD score. These data highlight potential predictive implications of Signature 3 to complement HRD and BRCA status in identifying patients who may benefit from exposure to platinum therapy. [Table: see text]