Real-world analysis of patients with advanced gastrointestinal (GI) cancers harboring inactivating TSC1 and TSC2 alterations using the Foundation Medicine genomic database.

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558 Background: Genomic profiling of GI tumors can identify potentially actionable genetic alterations, ultimately leading to better outcomes in patients who currently have few treatment options. In exploratory biomarker analyses of patients with perivascular epithelioid cell tumors treated with the mTOR inhibitor nab-sirolimus (AMPECT, NCT02494570), those with inactivating alterations in the tumor suppressor genes TSC1 or TSC2 (critical negative regulators of mTOR activity) had confirmed responses (8/9 patients with inactivating TSC2 alterations and 1/5 patients with inactivating TSC1 alterations). PRECISION 1, a currently enrolling tumor-agnostic study, will evaluate nab-sirolimus in patients with TSC1 or TSC2 alterations. To enumerate the frequency of these alterations in GI cancers, we analyzed data from a real-world genomic database. Methods: Next-generation sequencing (NGS) data from Foundation Medicine’s genomic database of patients with advanced cancer were analyzed using the FoundationInsights web-based platform to identify patients with GI cancers who had inactivating TSC1 or TSC2 alterations (short variants [base substitutions, insertions and deletions], rearrangements, and copy number deletions). Tumor mutational burden (TMB), microsatellite instability status and other mutations were also characterized in this group of patients. Results: As of 29 March 2022, tumor tissue NGS data were available for 5816 patients with GI cancers bearing alterations in TSC1 or TSC2. Of these, 1642 patients had at least one inactivating alteration. The GI tumor types that most frequently expressed inactivating alterations in TSC1 or TSC2 were hepatocellular carcinoma (alterations in 6.5%); colorectal adenocarcinoma (1.7%); gastrointestinal stromal tumors (1.7%); and cholangiocarcinoma (1.6%). Of all 1642 patients, 688 were female, and most (74%) were 51–80 years of age when the sample was obtained. Of patients with inactivating TSC1 and TSC2 alterations, 37.6% were in TSC1 and 62.9% were in TSC2 and included short variants (31.3% and 48.4%), rearrangements (2.7% and 6.6%), and copy number deletions (3.5% and 7.4%), respectively. TMB was low (<6 mutations/megabase) in 58% of patients, and most patients had microsatellite stable (MSS; 71.3%) tumors. Other commonly mutated genes in this cohort were TP53 (62.7%), APC (38.5%) and KRAS (30.4%). Conclusions: TSC1 and/or TSC2 alterations were commonly observed in GI cancers. These cancers were frequently microsatellite stable and of low TMB suggesting that these are actionable alterations that may be candidates for targeted therapy. This hypothesis is being tested in the PRECISION 1 (NCT05103358) trial which is open for enrollment or just-in-time clinical trial sites and available to patients with GI cancers harboring TSC1 or TSC2 alterations.