Temporal Variation in Urinary Volatile Organic Compounds in Response to Therapeutic Intervention in Esophageal Cancer Patients

Background Oesophageal cancer (OC) is the seventh leading cause of cancer-related mortality worldwide. Volatile organic compound (VOC) analysis, such as in urine, offers a non-invasive and clinically accepted approach for cancer detection and disease monitoring. However, little is known about how urinary VOCs change over the course of treatment. The SEATTLE study (Temporal variation in exhaled volatile organic compoundS in rEsponse to therApeuTic inTervention in oesophageaL cancer patiEnts) is to our knowledge, the first prospective study to investigate longitudinal urinary VOC changes in OC. Methods Between 2019 and 2023, 72 patients with oesophageal adenocarcinoma (OAC) were recruited from a regional tertiary referral centre in the USA. Urine samples were collected at four timepoints: (1) pre-treatment, (2) post-neoadjuvant therapy, (3) post-surgery, and (4) post-operative follow-up (6–12 months). VOC extraction will be performed using a bespoke headspace (HS) method via an autosampler system equipped with a gas-tight syringe to transfer VOCs onto thermal desorption (TD) tubes. TD tubes will be analysed by TD-gas chromatography-time-of-flight-mass spectrometry (TD-GC-TOF-MS). Following data pre-processing, reproducible and high-quality chromatographic peaks will be matched against the NIST 2017 library for compound identification. Results To assess intra-participant temporal variation, participants without baseline (visit 1) samples were excluded (n = 4). Among the included participants (n = 68), samples were available for visits 1 and 2 (n = 23), and all four timepoints (n = 21). Non-consecutive sampling was observed in the remainder, including visits 1 and 4 (n = 1) and visits 1, 2, and 4 (n = 21). Given the physiological impact of surgery (visit 3), post-surgical VOC changes will be interpreted with caution, as they may confound true temporal trends. Untargeted VOC analysis is currently underway and will be completed before the conference. Conclusion This protocol outlines a standardised and scalable approach for longitudinal urinary VOC profiling using HS-TD-GC-TOF-MS. This pilot study will provide the first evidence for the potential of urinary VOC biomarkers to track treatment response in OC. Findings will inform large validation studies and guide future work to assess the utility of this approach across international healthcare systems, including for recurrence detection following curative treatment, where temporal VOC patterns may differ due to country-specific treatment pathways.