Spanish Validation of KOQUSS-40 Questionnaire: Assessing QoL of Gastric Cancer Patients After Gastrectomy: SPQUSS-41

Background: Gastric cancer treatment often involves radical surgery, significantly impacting patients' quality of life (QoL), with symptoms ranging from gastrointestinal issues to emotional distress. Existing QoL questionnaires do not comprehensively address symptoms specific to gastric surgery. Objective: This study aims to translate, culturally adapt, and validate the KOQUSS-40 questionnaire into Spanish (SPQUSS-41), providing a specific tool to assess QoL in patients undergoing curative gastric cancer surgery. This will enhance personalized care, patient-clinician communication, and symptom management. Design: A prospective, multicenter cohort study under Spain's EURECCA Esophagogastric Cancer Project. The English version of KOQUSS-40 will serve as the basis for translation. The study will unfold in two phases: Phase 1 - Development: Translation to Spanish and expert panel review to create version 1. Pre-test with 20 patients for comprehension. Pilot test with 85 patients to refine and evaluate version 2. Phase 2 - Validation: Administration of the final version alongside EORTC QLQ-C30 and QLQ-STO22. A retest will be conducted after 30 days to assess test-retest reliability. Study Population: Adults (\>18 years) who underwent curative gastric cancer surgery, from 1 month to 5 years post-op. Inclusion criteria: Surgery with curative intent, consent to EURECCA and SPQUSS-41 studies. Exclusion criteria: Other malignancies, advanced/metastatic disease, palliative surgery, or prior QoL questionnaires related to gastric cancer. Data Collection: Demographic and clinical-pathological data will be collected, including surgery type, lymphadenectomy, pathological stage, and oncologic treatment. Data will be recorded in the EURECCA online registry using a 6-digit patient code. Sample Size: Following the "rule of 10," at least 410 patients are required (10 patients per item, 41 items). A test-retest sample of 381 patients is planned, with expected participation from at least 10 centers over 1-2 years. Statistical Analysis: Descriptive statistics for demographic/clinical variables. Construct validity via principal component analysis. Criterion validity using Pearson correlations and EORTC questionnaires. Internal consistency via Cronbach's alpha. Test-retest reliability via Spearman correlation and Cohen's weighted kappa. Analysis in SPSS 28.0; significance at p \< 0.05. Work Plan - Six Work Packages: WP1: Study protocol, ethics approval, trial registration, and database setup. WP2: Initial translation and expert consensus (Version 1). WP3: Pre-test with 20 patients and refinement (Version 2). WP4: Pilot test with 85 patients using Version 2 and reference tools. Final expert review to establish the final version. WP5: Launch validation phase across centers. Administer final questionnaire to 410 patients and conduct retest with 381. WP6: Data analysis, manuscript preparation, and dissemination of validated SPQUSS-41 questionnaire in Spanish.