A Look at ctDNA Monitoring in Small Cell Lung Cancer

Small Cell Lung Cancer: Small Cell Lung CancerSmall cell lung cancer (SCLC), known for its aggressive nature and limited treatment options, presents a significant clinical challenge. A commentary published in AACR's Clinical Cancer Research reviewed research that suggests circulating tumor DNA (ctDNA) monitoring could hold promise as a valuable tool in managing extensive-stage SCLC (ES-SCLC) (2023; https://doi.org/10.1158/1078-0432.CCR-23-0420). This study's findings provide insights into ctDNA's role in predicting clinical responses and survival outcomes in ES-SCLC patients. Researchers, led by Lavanya Sivapalan, PhD, a Postdoctoral Research Fellow at Johns Hopkins University, along with colleagues, conducted a comprehensive investigation into ctDNA dynamics in ES-SCLC. The study involved 33 ES-SCLC patients, as well as cutting-edge techniques such as targeted error-correction sequencing, were employed to analyze ctDNA levels. Matched peripheral blood mononuclear cell (PBMC) sequencing from 32 of these patients was also performed to enhance the specificity of ctDNA analysis. One of the study's key findings is the robust correlation between ctDNA dynamics and clinical responses, as well as survival outcomes. The research classified ctDNA dynamics into three distinct groups: molecular response (complete ctDNA elimination), molecular response followed by recrudescence (initial ctDNA elimination followed by resurgence), and molecular progression (persistent ctDNA levels). These patterns strongly correlated with progression-free survival, overall survival, durable clinical benefit, and radiological findings. The study emphasized the importance of matched PBMC DNA sequencing to improve ctDNA analysis accuracy. Without this step, certain mutations derived from clonal hematopoiesis might lead to false-positive results. Filtering out these mutations through matched PBMC sequencing is crucial for precise prognostic assessments. Contextualizing ctDNA Prior research has explored ctDNA's potential in SCLC, demonstrating its ability to predict disease progression and therapeutic responses. However, this study stands out by integrating genome-wide copy number alteration status into ctDNA analysis. This addition allows for the assessment of molecular responses in patients without identifiable tumor-specific mutations in plasma. While the study's findings are promising, several challenges remain. Standardizing ctDNA analysis time points and optimizing gene panels to better capture SCLC's genomic characteristics are essential steps for clinical application. Moreover, determining how ctDNA data can be effectively integrated into clinical decision-making is crucial. Currently, ES-SCLC treatment options are limited and knowing early responses through ctDNA monitoring may not substantially influence treatment decisions. Oncology Times chatted with senior study author, Aadel Chaudhuri, MD, PhD, for additional insights into ctDNA's evolving role in ES-SCLC. He is Assistant Professor of Radiation Oncology at Washington University School of Medicine and Liquid Biopsy Working Group Leader with Siteman Cancer Center at Barnes-Jewish Hospital. Oncology Times: The study introduced a new ctDNA response category—“initial response followed by recrudescence.” What are the implications of this finding and how might it impact patient management? Chaudhuri: “Molecular response followed by recrudescence refers to a ctDNA dynamic pattern where the ctDNA is initially eliminated after starting treatment, but then later re-emerges and becomes detectable again. These patients had intermediate survival outcomes compared to patients who had sustained elimination of ctDNA, and those where ctDNA persisted across all timepoints. While not terribly surprising, the study by Sivapalan, et al, was able to identify this new response pattern by serially monitoring ctDNA across multiple time points, thus setting it apart from earlier studies in the small cell lung cancer ctDNA space. “The implications are that serial sampling of ctDNA in small cell lung cancer patients appears to be prognostically valuable. Ultimately, it will be important to determine if the recrudescent ctDNA after initial elimination can again be systematically ablated to further improve patient outcomes, thus facilitating a ctDNA-centric way to manage small cell lung cancer and improve survival outcomes for this deadly disease.” Oncology Times: Considering the current limited therapeutic options for ES-SCLC, how might ctDNA data be used to inform personalized treatment decisions and what are the challenges in implementing such an approach? Chaudhuri: “Indeed, because SCLC has a limited therapeutic armamentarium, it would be challenging for ctDNA to inform personalized treatment decision-making, as it is unlikely that the oncogenomic information from ctDNA would help identify drugs that target cancer-specific alterations (unlike lung adenocarcinoma which has a reasonably sized armamentarium of precision therapeutics). “Still, ctDNA could potentially inform personalized treatment decision-making for extensive-stage small cell lung cancer as we highlighted...where ctDNA persistence despite combination chemotherapy and immunotherapy could inform second-line investigational agents, and ctDNA elimination on-treatment could enable treatment-free surveillance in select patients.” Oncology Times: The conclusion of the study suggests that ctDNA is not yet ready for prime-time use in SCLC. What is needed to determine the clinical utility of ctDNA-based monitoring in this context, and what are the potential implications for patient care? Chaudhuri: “We need studies that compare ctDNA-guided treatment paradigms to standard-of-care treatment paradigms. If these studies are successful, then we will have evidence showing that ctDNA-based monitoring can personalize treatment and improve survival outcomes for extensive-stage small cell lung cancer patients.” Dibash Kumar Das is a contributing writer.