LAUSR

3136 Background: Personalizing therapy will arguably have no greater impact than on patients (pts) with rare (< 6 per 100,000 population) or less common cancers (6-12/100,000). MoST combines a molecular screening platform and biomarker-driven treatments for pts with advanced cancer, with a particular focus on rare and less common cancers (RLC). Methods: Molecular screening was performed using in-house and commercial panels on archival tumor tissue. A Molecular Tumor Board by consensus reported on pathogenic variants with potential therapeutic actionability. Tiers of actionability were defined as: Tier 1–eligible for a MoST substudy; Tier 2–clinical evidence of efficacy in any cancer type, Tier 3—preclinical evidence. The clinical and molecular characteristics of the first 1,000 pts are presented here. Results: Pts were recruited from Sept 2016 to Dec 2018. A report was issued in 94% of cases in a median of 7.7 weeks from consent. In 6%, there was insufficient tissue. The median age at cancer diagnosis was 35 years (range 4-85 years), and 49% were male. Pts had a median of 2 lines of prior systemic therapy (0-11), and a median baseline ECOG performance status of 0 (range 0-3). 82% of pts had RLCs. A total of 2642 pathogenic variants were reported, of which 1144 (43%) were deemed therapeutically actionable. 651(57%) of actionable variants (AVs) occurred in RLC (Table). Most commonly, AVs were found in the cell cycle, homologous recombination repair (HR) and fibroblast growth factor (FGF) pathways. 559(66%) of pts had at least one AV identified, 30% tier 1, 63% tier 2 and 6% tier 3, including 66% of RLC. In 30% of cases, a tumor mutational burden >11 mutations/ megabase was reported. Conclusions: Here we report a high frequency of AVs in RLC, providing a rational basis for assessing the potential of personalized therapy in a population with a historically unmet need for effective treatment. Clinical trial information: ACTRN12616000908437. [Table: see text]