Usefulness of indigo carmine chromoendoscopy for detecting gastric cancer and gastric adenoma during upper gastrointestinal endoscopy (INDIGO study): protocol for a prospective multicentre observational study.

Abstract

Introduction: Early gastric cancer is characterised by subtle mucosal and colour changes that frequently lead to missed lesions during routine endoscopy, making detection difficult. Indigo carmine spraying is a classical chromoendoscopic method to enhance mucosal surface irregularities and has been believed to have the potential to facilitate the detection of early gastric neoplasia. This method is widely used in Japan; however, whether it improves gastric neoplasm detection remains unclear. In this prospective study, we aim to evaluate the usefulness of indigo carmine spraying for detecting gastric cancer and gastric adenoma during upper gastrointestinal endoscopy in patients at high risk of gastric cancer.

Methods and analysis: This prospective multicentre observational study will include over 30 institutions. Patients undergoing upper gastrointestinal endoscopy for surveillance after endoscopic treatment or pretreatment screening will be enrolled. The age range has been set from 20 years to 95 years, and patients for whom a biopsy will not be feasible will be excluded. Gastric observation will consist of two steps: the first will use white light imaging, followed by a second-pass observation after spraying 20-40 mL of indigo carmine at a concentration of 0.1-0.4%. The primary endpoint will be the proportion of patients with gastric cancer or adenoma lesions detected during the second-pass observation among those who undergo successful indigo carmine examination. A one-sided binomial test (α=0.05) will be used to compare the detection rate with a predefined threshold of 1.0%. We aim to enrol a total of 1050 patients to achieve 80% power.

Ethics and dissemination: This study was approved by the Institutional Review Board of Kanagawa Cancer Center (approval number: 2025-92). Written informed consent will be obtained at the time of registration. Following completion of this research, the findings will be promptly compiled and published in appropriate academic conferences and peer-reviewed international journals.

Trial registration number: UMIN000059685.