To the Editor: Pediatric lung adenocarcinoma is extremely rare, often presents with metastatic disease, and portends a poor prognosis with a median survival of 14 months and a 5-year survival rate of 26% 1-4. Molecular diagnostics have become essential in pediatric non–small cell lung cancer (NSCLC) management 2, 5-7, including the detection of EGFR, BRAF, and MET mutations and ALK, ROS1, RET, and NTRK translocations 5, 8, enabling the implementation of kinase inhibitors into front-line treatment leading to improved outcomes 5, 8. Recently, noninvasive “liquid biopsies” for plasma circulating tumor DNA (ctDNA) have been studied as an emerging biomarker in NSCLC that correlates with tumor volume and risk subtype at diagnosis 9. Although recent studies suggest the potential diagnostic and prognostic value of plasma ctDNA in NSCLC, it has not been incorporated into standardized NSCLC treatment response and surveillance guidelines to inform management decisions due to the heterogeneity of assays used, lack of standardized follow-up timepoints, and suboptimal sensitivity of current assays 10. A 16-year-old never-smoker girl with no significant past medical history presented to the emergency department with two months of progressive shortness of breath, decreased exercise tolerance, progressively worsening productive cough, intermittent fevers, fatigue, unintentional weight loss, and pleuritic chest pain. Positron emission tomography (PET) demonstrated a hypermetabolic mediastinal mass with contiguous right upper lobe pulmonary involvement encasing the superior vena cava (SVC), with flattening of the distal trachea and narrowing of the right mainstem bronchus, and multiple hypermetabolic right upper lobe pulmonary lesions in addition to hypermetabolic osseous, hepatic, and local and distant lymph node metastases (Figure 1A–C). Chest computed tomography (CT) demonstrated a mediastinal mass with mass effect on the trachea, SVC, and right mainstem bronchus with diffuse lymphadenopathy, in addition to hepatic hypodensities and heterogeneous appearance of the bone marrow at the vertebral body of T7. There was no evidence of metastatic brain lesions on the brain MRI. A left supraclavicular lymph node was biopsied and demonstrated portions of partially encapsulated fibrous tissue nearly entirely involved by a proliferation of medium to large malignant-appearing cells. Lesional cells had abundant pale mucinous to eosinophilic cytoplasm with large nuclei and prominent nucleoli growing in sheets and nests, and in many areas, also showed micropapillary formation (Figure 2A). Immunostaining performed across multiple institutions showed tumor cells in the lymph node to be positive for pancytokeratin, CK7, TTF-1, and Napsin A, with diffuse weak staining for ALK (D5F3 clone), and the presence of intracytoplasmic mucin was confirmed by mucicarmine cytochemical staining (Figure 2B–E). Overall, the morphology and immunoprofile with radiologic imaging data were consistent with a diagnosis of stage IV moderately differentiated lung adenocarcinoma. The RNA fusion panel of the metastatic supraclavicular lymph node lesion demonstrated an EML4::ALK fusion. Given the detectable EML4::ALK fusion, the patient was started on alectinib 600 mg BID, as alectinib has demonstrated superior CNS disease-free survival compared to platinum-based chemotherapy 11 and superior progression-free survival, lower rates of CNS progression, and reduced toxicity compared to crizotinib in previously untreated adults with advanced stage ALK-rearranged NSCLC, including patients diagnosed with stage IV disease 12. Two weeks after initiation of alectinib therapy, the EML4::ALK fusion was detected by Caris Assure circulating nucleic acid sequencing (cNAS; Supplementary Table S1). The patient remained adherent to alectinib and interval chest computed tomography (CT) scans and whole-body PET scans obtained at 2 and 4 months after starting alectinib therapy demonstrated a partial response (PR) in pulmonary and metastatic disease as per RECIST criteria (at least 30% decrease in sum of diameters of target lesions with no new target lesions) and brain MR continued to be negative for metastatic brain lesions. After 8.5 months of alectinib therapy, chest CT and whole-body PET continued to show an improved PR as per RECIST criteria with no evidence of pulmonary disease and with a residual hypermetabolic hepatic focus (Figure 1D–F). At the same time point, Caris Assure cNAS testing showed loss of EML4::ALK fusion detection (Supplementary Table S1). After 14 months of alectinib therapy, chest CT and whole-body PET demonstrated a complete response (CR) as per RECIST criteria (disappearance of all target lesions and pathological lymph nodes <10 mm in short axis; Figure 1G–I) and Caris Assure cNAS continued to demonstrate loss of EML4::ALK fusion detection (Supplementary Table S1). The high-sensitivity plasma cNAS (Caris Assure) assay used in this report addresses key barriers to ctDNA analysis as a standardized approach for targeted therapy selection and response monitoring, including correlation of radiographic response with loss of EML4::ALK fusion detection on cNAS. Analysis of both cell-free DNA and RNA from the plasma enhances the detection of clinically relevant alterations, and incorporation of paired white blood cell (WBC) sequencing enables discrimination of true tumor-derived variants from false positives, such as those arising from clonal hematopoiesis (CH), ultimately improving the reliability and clinical interpretability of results 10, 13. This cNAS method enables comprehensive whole-exome and transcriptome analysis of tumor-derived alterations, including detection of de novo and compound mutations in oncogenic drivers, kinase fusions, and alterations in off-target pathways 13. This allows for the identification of resistance mechanisms to specific kinase inhibitors prior to the onset of symptoms or radiographic evidence of progression or relapse 13. This report supports the need for further studies to evaluate how detection and subsequent loss of oncogenic drivers with a high-sensitivity cNAS assay correlates with radiographic response to targeted therapy at standardized intervals in receptor tyrosine kinase (RTK)-mutated and kinase fusion-driven pediatric malignancies. The authors confirm that there are no conflicts of interest. The authors confirm that written consent for submitting and publishing this case report, including images and associated text, has been obtained from the patient's family. There are no identifiers included in this report. A.D.G. is supported by NIH grant 2T32CA009615, and T.W.L. is supported by the Alex's Lemonade Stand Foundation Center of Excellence and NIH grant 1R50CA305079. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Guerra et al. (Sat,) studied this question.