Abstract 728: Early assessment of treatment effect in small cell lung cancer (SCLC) via ctDNA analysis

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Abstract INTRODUCTION: Quantifying circulating tumor DNA (ctDNA) is an emerging method to non-invasively assess treatment effect for solid tumors. A ctDNA-based method for disease monitoring for small cell lung cancer (SCLC) would be beneficial to disease management. By employing plasma taken during early treatment cycles and NGS, we tested whether early response assessed by ctDNA level could predict treatment effect. METHODS: Using a 197-gene NGS assay, the AVENIO ctDNA Surveillance Kit (for Research Use Only, not for use in diagnostic procedures), ctDNA levels were assessed in post-treatment plasma samples based on variants identified at baseline. Mutant allele concentration or mutant molecules per milliliter-of-plasma (MMPM) was utilized to quantify ctDNA over all variants of all sequenced genomic regions. Samples collected from an observational German Lung Cancer Multi-Marker Study were analyzed retrospectively. In a cohort of 69 stage IV SCLC subjects, the association of survival with ctDNA-based monitoring classifier was evaluated in the first available post-treatment plasma sample after starting chemotherapy (median number of days after start of treatment = 25) by Kaplan-Meier methods and Cox proportional hazards model. RESULTS: The analysis demonstrated that subjects with mean MMPM less than the lower quartile (14.3) had longer progression free survival (PFS) compared to that of subjects with mean MMPM greater than or equal to the lower quartile (log-rank P = 0.0095; HR [95% CI] = 0.48 [0.27, 0.84]). The same classifier was applied for overall survival analysis, and subjects with mean MMPM less than the lower quartile had longer overall survival (OS) compared to that of subjects with mean MMPM greater than or equal to the lower quartile (log-rank P = 0.0095; HR [95% CI] = 0.46 [0.26, 0.84]). CONCLUSIONS: Changes in ctDNA levels in response to treatment may prove to be a valuable way of identifying subjects that either respond or fail to respond to therapy earlier than current standard of care methods such as computed tomography (CT) scan. Hypotheses will be validated in a separate cohort. Future prospective studies to confirm these results are needed. Citation Format: John Jiang, Christine Ju, Corinna Woestmann, Aarthi Balasubramanyam, Liu Xi, Stephanie J. Yaung, Sandeep Gattam, Bernd Hinzmann, Michael Thomas, Felix Lasitschka, Michael Meister, Marc Schneider, Felix Herth, Thomas Muley, Birgit Wehnl, John Palma. Early assessment of treatment effect in small cell lung cancer (SCLC) via ctDNA analysis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 728.

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