Using circulating tumor DNA analysis to depict genomic profiles and predict survival outcomes in patients with small-cell lung cancer.

8567 Background: Small-cell lung cancer (SCLC) accounts for approximately 15% of lung cancers. Most patients have extensive-stage disease with widespread metastases and poor survival. Understanding the molecular mutation profile of each SCLC patient would allow precision treatment and improved clinical outcome. However, tumor tissues from surgery are not available for most SCLC patients and biopsy specimens are often have limited quantities. Several studies have provided evidence of circulating tumor DNA (ctDNA) in detecting somatic variants of multiple solid tumors. This study evaluated utility of ctDNA to depict genomic profiles and predict survival outcomes in SCLC patients. Methods: 22 Plasma samples were obtained before initial treatment from 22 patients with SCLC enrolled between 2012 and 2016. Targeted-capture deep sequencing was performed to identify somatic variants in 465 cancer-related genes. Genomic mutation profiles were described and the clinical implications were further analyzed. Results: Tumor DNA can be detected in all 22 plasma samples collected from patients with SCLC. In total, 340 variants were identified, and the mean and median mutation rate were 6.3 and 6.6 per Mb. TP53 and RB1 are the most frequently mutated genes, detected in 90.9% (20/22) and 59.1% (13/22) patients, respectively. Further analysis showed that high ctDNA fraction in cell-free DNA (cfDNA) was associated with heavy tumor burden (R = 0.7, p = 0.0017). Moreover, patients with high ctDNA fractions (ctDNA fraction > = 18.3%) had poor progression free survival (PFS) (HR, 17.2; p = 0.0019). The median PFS of patients with high versus low ctDNA fractions was 5.2 months (95% CI 4.6 to 5.8 months) versus 10.0 months (95% CI 9.3 to 10.7 months), respectively. Conclusions: In this study, ctDNA analysis offers a promising way to depict the molecular profile in patients with SCLC. Moreover, these findings highlight the potential clinical utility of ctDNA to predicate clinical outcome in SCLC.