Retrospective study wrongly claimed prospective validation, letter warns

A letter published in Cancer Imaging reports that a study on early tumour shrinkage in esophageal squamous cell carcinoma misdescribed both its own study design and its validation status, and contains a numerical inconsistency in its responder counts.

The correspondence, authored by Ehsan Khodamoradi and published on 21 October 2026, addresses an article by Zhou et al. that examined the prognostic value of early tumour shrinkage (ETS) and depth of response (DoR) in patients with esophageal squamous cell carcinoma.

According to the letter, the Methods section of the original article states that the study retrospectively analyzed 125 patients, yet the Introduction and Discussion claim that the study prospectively validated the prognostic value of ETS and DoR.

The letter explains that 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.

Khodamoradi also challenges the original authors’ conclusion that they developed and validated a comprehensive predictive model. The letter states that no external validation, temporal validation, or clearly described internal validation procedure is reported in the article.

A further methodological concern raised in the correspondence concerns the thresholds used to classify patients. The ETS and DoR cut-offs were derived from ROC analysis within the same cohort and then applied to the same patients for survival analysis, an approach the letter says risks overfitting and optimistic bias.

The letter additionally identifies a numerical inconsistency in the reported results. The Results section of the original article describes responders (n = 109) and non-responders (n = 12), while the corresponding results listed by Zhou et al. give the ratio as 12/109, reversing the group labels.

In closing, the correspondence suggests 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, noting that such corrections would uphold the integrity of the scientific literature.

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

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

Article References: Khodamoradi, E. (2026). Misreporting of study design and validation status in a study of early tumour shrinkage in esophageal squamous cell carcinoma. Cancer Imaging, 26(1), Article 148. https://doi.org/10.1186/s40644-026-01146-1

Image Credits: AI Generated

DOI: 10.1186/s40644-026-01146-1

Keywords: esophageal squamous cell carcinoma, early tumour shrinkage, depth of response, retrospective study, prospective validation, study design, ROC analysis, overfitting, predictive model, research integrity, Cancer Imaging, correspondence