HER2 Copy Number and Resistance Mechanisms in Patients with HER2-positive Advanced Gastric Cancer Receiving Initial Trastuzumab-based Therapy in JACOB Trial

Resistance mechanisms; Advanced gastric cancer; TrastuzumabMecanismos de resistencia; Cáncer gástrico avanzado; TrastuzumabMecanismes de resistència; Càncer gàstric avançat; TrastuzumabPurpose: In JACOB trial, pertuzumab added to trastuzumab-chemotherapy did not significantly improve survival of patients with HER2-positive metastatic gastric cancer, despite 3.3 months increase versus placebo. HER2 copy-number variation (CNV) and AMNESIA panel encompassing primary resistance alterations (KRAS/PIK3CA/MET mutations, KRAS/EGFR/MET amplifications) may improve patients’ selection for HER2 inhibition. Experimental Design: In a post hoc analysis of JACOB on 327 samples successfully sequenced by next-generation sequencing (NGS; Oncomine Focus DNA), HER2 CNV, HER2 expression by IHC, and AMNESIA were correlated with overall response rate (ORR), progression-free survival (PFS), and overall survival (OS) by univariable/multivariable models. Results: Median HER2 CNV was 4.7 (interquartile range, 2.2–16.9). HER2 CNV-high versus low using the median as cutoff was associated with longer median PFS (10.5 vs. 6.4 months; HR = 0.48; 95% confidence interval: 0.38–0.62; P < 0.001) and OS (20.3 vs. 13.0 months; HR = 0.54; 0.42–0.72; P < 0.001). Combining HER2 CNV and IHC improved discriminative ability, with better outcomes restricted to HER2-high/HER2 3+ subgroup. AMNESIA positivity was found in 51 (16%), with unadjusted HR = 1.35 (0.98–1.86) for PFS; 1.43 (1.00–2.03) for OS. In multivariable models, only HER2 CNV status remained significant for PFS (P < 0.001) and OS (P = 0.004). Higher ORR was significantly associated with IHC 3+ [61% vs. 34% in 2+; OR = 3.11 (1.89–5.17)] and HER2-high [59% vs. 43% in HER2-low; OR = 1.84 (1.16–2.94)], with highest OR in the top CNV quartile. These biomarkers were not associated with treatment effect of pertuzumab. Conclusions: HER2 CNV-high assessed by NGS may be associated with better ORR, PFS, and OS in a JACOB subgroup, especially if combined with HER2 3+. The negative prognostic role of AMNESIA requires further clinical validation

BRCA2 Germline Mutations Identify Gastric Cancers Responsive to PARP Inhibitors

Mutations; Gastric cancers; PARP inhibitorsMutacions; Càncers gàstrics; Inhibidors de PARPMutaciones; Cánceres gástricos; Inhibidores de PARPDespite negative results of clinical trials conducted on the overall population of patients with gastric cancer, PARP inhibitor (PARPi) therapeutic strategy still might represent a window of opportunity for a subpopulation of patients with gastric cancer. An estimated 7% to 12% of gastric cancers exhibit a mutational signature associated with homologous recombination (HR) failure, suggesting that these patients could potentially benefit from PARPis. To analyze responsiveness of gastric cancer to PARPi, we exploited a gastroesophageal adenocarcinoma (GEA) platform of patient-derived xenografts (PDX) and PDX-derived primary cells and selected 10 PDXs with loss-of-function mutations in HR pathway genes. Cell viability assays and preclinical trials showed that olaparib treatment was effective in PDXs harboring BRCA2 germline mutations and somatic inactivation of the second allele. Olaparib responsive tumors were sensitive to oxaliplatin as well. Evaluation of HR deficiency (HRD) and mutational signatures efficiently stratified responder and nonresponder PDXs. A retrospective analysis on 57 patients with GEA showed that BRCA2 inactivating variants were associated with longer progression-free survival upon platinum-based regimens. Five of 7 patients with BRCA2 germline mutations carried the p.K3326* variant, classified as “benign.” However, familial history of cancer, the absence of RAD51 foci in tumor cells, and a high HRD score suggest a deleterious effect of this mutation in gastric cancer. In conclusion, PARPis could represent an effective therapeutic option for BRCA2-mutated and/or high HRD score patients with GEA, including patients with familial intestinal gastric cancer.This work was funded by the Italian Association for Cancer Research (AIRC), IG 20210 and IG 27531 to S. Giordano; IG 23624 to F. Pietrantonio; IG 21770 to S. Corso. FPRC 5×1000 2015 Min. Salute “Strategy” to SG; Fondazione Piemontese per la Ricerca sul Cancro (FPRC) 5×1000 MS2017 PTCRC-intra 2020 to S. Giordano; Ricerca Locale Dept. Oncology 2021 to S. Corso; Italian Ministry of Health-Ricerca Corrente 2022–23. B. Pellegrino was supported by ESMO with a Clinical Translational Fellowship aid supported by Roche and received research grants from GOIRC. Fondazione CR Firenze to M. Benelli

The Tumor-Specific Expression of L1 Retrotransposons Independently Correlates with Time to Relapse in Hormone-Negative Breast Cancer Patients

Background: Long-Interspersed Nuclear Element (L1) retrotransposons are silenced in healthy tissues but unrepressed in cancer. Even if L1 reactivation has been associated with reduced overall survival in breast cancer (BC) patients, a comprehensive correlation with clinicopathological features is still missing. Methods: Using quantitative, reverse-transcription PCR, we assessed L1 mRNA expression in 12 BC cells, 210 BC patients and in 47 normal mammary tissues. L1 expression was then correlated with molecular and clinicopathological data. Results: We identified a tumor-exclusive expression of L1s, absent in normal mammary cells and tissues. A positive correlation between L1 expression and tumor dedifferentiation, lymph-node involvement and increased immune infiltration was detected. Molecular subtyping highlighted an enrichment of L1s in basal-like cells and cancers. By exploring disease-free survival, we identified L1 overexpression as an independent biomarker for patients with a high risk of recurrence in hormone-receptor-negative BCs. Conclusions: Overall, L1 reactivation identified BCs with aggressive features and patients with a worse clinical fate