Abstract 3814: Molecular background conditioning by temozolomide in neuroendocrine tumors

Abstract Temozolomide (TMZ)-based regimens represent a valid therapeutic option in well-differentiated neuroendocrine tumors (NETs G2 and G3). As an alkylating agent, it increases DNA alteration by altering guanine residues, which either triggers cell death or results in novel missense mutations especially in MGMT deficient cells. Here, we describe an exploratory case series of TMZ-treated NETs cases that underwent NGS analysis at the University Hospital of Verona. Methods. We included 32 patients (16 G2 and 16 G3). NGS was performed before TMZ treatment for 22 cases (54%), after for 19 (46%) and in both for 4 cases (13%). We performed NGS on tissue samples for 73% of assays and via liquid biopsy for the remaining 27%. For tissue NGS, in 77% of samples we used an in-house panel encompassing 174 genes and in 23% commercial test interrogating at least 500 genes. Only ACMG/AMP class IV-V molecular alterations were considered for further analysis. Main Results From 2021 we performed NGS analysis on 32 NETs (G2 and G3) treated with TMZ-based regimes. Most cases (28 pf 32, 84.4%) were pancreatic NETs. Mean Ki-67 at baseline was 24.5% (range 3-60). The mean number treatments prior to TMZ were 1.4 and 0.5 between CAPTEM and subsequent NGS. The top five altered genes at baseline were MEN1 (32%), TP53 (14%), DAXX (14%), PTEN (9%) and SMAD4 (9%). None of the patients showed a high TMB (>15Mut/Mb) at baseline, while 26% of post-TMZ samples displayed that feature. Mean TMB at baseline and after treatment was 6,51 (range 1-10.6) and 22,9 mut/Mb (range 1-216) respectively. Alterations in DDR systems genes, including ATM, ATR, CHEK2, BRCA1, BRCA2, MLH1, MLH2, PMS2 MLH6 and MUTYH, were found in 8 patients (47%) after TMZ exposure; only one DDR-specific alteration (MUTYH) was found at baseline. DDR defects were enriched in patients exposed to higher numbers of treatments. The increase in mean TMB and enrichment in mutations in the DDR system is also confirmed when analysing the 6 cases having both pre- and post-TMZ treatment samples. Among other pathways, cell cycle deregulating genes (CDKN1A, CDKN2B, CDKN1B, CDK12, CDK6, RB1) were altered in 2 (11%) and 5 (29%) pre- and post-TMZ NGS samples respectively, the mTOR pathway (MTOR, NF1, PIK3CA, AKT, TSC1, TSC2, PTEN) in 2 (11%) and 8 (47%), and the MAPK pathway (KRAS and BRAF) in 1 (5%) and 2 (12%). Conclusions. The wide and effective use of temozolomide in neuroendocrine tumors, together with the potential therapeutic implications of DDR defects make this topic of great interest. The DDR pathway was one of the most affected by alterations in post-TMZ samples, although the genotoxic agent caused a general increase in the rate of somatic mutation. The status of DDR systems, either germinal or somatic, may represent an important selection and/or stratification parameter for future immunotherapy clinical studies also in neuroendocrine tumours provided that the analysis is carried out in a systematic, comprehensive and longitudinal way. Citation Format: Elena Trevisani, Anna Reni, Irene Torresan, Alice Rossi, Michele Borghesani, Silvia Nicolini, Claudio Luchini, Luca Landoni, Davide Melisi, Aldo Scarpa, Michele Milella, Andrea Mafficini, Sara Cingarlini. Molecular background conditioning by temozolomide in neuroendocrine tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3814.