De novo EGFR T790M mutations in a community-based oncology practice.

• DOI: 10.1200/jco.2022.40.16_suppl.3146
• Publication Date: 2022-06-06T16:09:21Z
• Authors: Marilyn Elaine Holt; Amanda Misch; Smita K. Rao; Emma Sturgill; Carissa Jones; Daniel Schlauch; Daniel Luckett; David R. Spigel; Suzanne Fields Jones; Andrew Jacob McKe...
• Keywords: T790M; Osimertinib

3146 Background: With the 2018 FDA approval of osimertinib for first-line treatment in EGFR-mutated lung cancers, prevalence acquired EGFR T790M mutations is expected to decrease, heightening significance de novo mutations. Previous studies have reported a wide range prevalence, and smaller retrospective indicated that germline may comprise majority Here, we assess frequency community-based setting report on occurring within this population. Methods: Patients with T790M-positive cancer were identified using Sarah Cannon’s clinicogenomics database containing information patients treated Cannon research network. All detected tissue- plasma-based NGS tests delivered as part routine care. De status was determined via manual electronic health record chart review. When available, allele fraction %cfDNA values extracted from structured analyzed separately. Results: Of cancers available pretreatment testing results, 36% (16/44) confirmed be T790M+ prior TKI exposure; five these received testing, all originated germline. Two ordered by external providers added our patient analysis after Co-occurring mutations, including L858R, pre-TKI samples 78% (14/18) (Table). TP53, KRAS, PTEN, or RB1 without co-occurring C797S observed one four post-TKI results. cases frequencies, 100% (4/4) had fractions >0.5 (tissue) and/or >50% (plasma). Average higher (allele fraction: 0.5 ± 0.2; %cfDNA: 40% 20%) than 0.3 2% 2%). Conclusions: Roughly one-third real-world settings occur before exposure associated inheritance. Allele potential indicator scenarios where pre-treatment data not available. Future will investigate impact response evolution resistance mechanisms osimertinib-treated patients. [Table: see text]