Misreporting of study design and validation status in a study of early tumour shrinkage in esophageal squamous cell carcinoma.

This letter to the Editor addresses a fundamental inconsistency in the reporting of study design and validation status in the article by Zhou et al. published in Cancer Imaging. The authors state in the Methods section that the study retrospectively analyzed 125 patients, yet the Introduction and Discussion claim that the study prospectively validated the prognostic value of early tumour shrinkage (ETS) and depth of response (DoR). Prospective validation requires a priori model specification and evaluation on subsequently collected data, whereas retrospective analyses are inherently susceptible to selection bias and cannot establish prospective validity. The authors also conclude that they developed and validated a comprehensive predictive model, but no external validation, temporal validation, or clearly described internal validation procedure is reported. The ETS and DoR thresholds were derived from ROC analysis within the same cohort and then applied to the same patients for survival analysis, risking overfitting and optimistic bias. Additionally, the Results report "responders (n = 109) and non-responders (n = 12)," while the corresponding results in the original article by Zhou et al. [1] list the ratio as 12/109, reversing the group labels. We respectfully suggest that the authors clarify the actual study design, remove any claim of prospective validation if the study is retrospective, provide evidence of validation or remove the claim of a validated model, and correct the numerical inconsistency. Such corrections would uphold the scientific integrity of the literature.