Pathological complete response, often abbreviated pCR, is one of the most coveted outcomes in modern oncology. It means that when pathologists examine the surgically removed tumor under the microscope, no viable cancer cells remain, suggesting that the preoperative treatment eliminated the disease entirely. With the arrival of immune checkpoint inhibitors, a growing share of esophageal squamous cell carcinoma patients are now achieving this outcome, and oncologists are increasingly confronted with a practical question: once a patient has reached pCR, how intensively should they be followed after surgery? The original study by Zhang and colleagues attempted to answer this by identifying clinical factors associated with disease-free survival and overall survival in this favorable subgroup, proposing a three-factor model to stratify patients for individualized postoperative surveillance.

That model, however, is precisely where the commentary directs its technical criticism. Sengan and Ramaiah point out that the multivariable Cox regression combined three variables into a single risk-factor triad, but those variables were not drawn from the same underlying sample. Clinical T stage was recorded only for the 100 patients with complete pretreatment imaging, whereas the neoadjuvant cycle count and the interval between treatment and surgery were available across the full 154-patient cohort. By restricting the entire model to the imaging-complete subset, the authors argue, the reported hazard ratios for cycle count and treatment-to-surgery interval reflect a different and smaller sample than the one in which those two variables were originally identified as candidates, in work stemming from the NEXUS-1 phase II trial of conversion immunochemotherapy.

The excluded 54 patients matter for more than arithmetic reasons. According to the commentary, these patients were treated at outside institutions where preoperative staging was less rigorously documented, which introduces a plausible link between exclusion and unmeasured disease severity. This is the classic structure of collider bias, a phenomenon in which conditioning on a shared consequence, in this case having complete imaging data, can induce spurious associations or mask real ones. The commentators acknowledge that the original study explicitly flagged the potential for collider bias in its pCR-restricted analysis, an act of caution they describe as rare and commendable in retrospective series. But they contend that presenting cycle count and treatment-to-surgery interval as co-equal predictors alongside T stage in a single table implies comparable evidentiary weight when, in fact, the T stage estimate alone required the restricted subgroup while the other two associations could have been tested in the full cohort with T stage omitted from that model.

The deeper problem, the commentary argues, is one of statistical power. Across all 154 patients, only 20 recurrences and 14 deaths were observed, and the number of disease-free survival events would be still fewer once deaths without recurrence were excluded. Against this meager event total, the original study screened 11 candidate variables in univariable Cox regression and retained four for multivariable modeling on the further-restricted 100-patient subset. Standard guidance for Cox regression recommends at least ten events per covariate to obtain stable hazard ratio estimates, meaning a four-covariate model would ideally rest on roughly 40 events. A model built on an event count in the range of 15 to 20 falls well short of that threshold, a deficiency that the commentators say is plainly visible in the reported confidence intervals. The hazard ratio for the treatment-to-surgery interval carried a 95 percent confidence interval spanning 1.198 to 23.840, and the interval for cycle count stretched from 1.168 to 10.179, ranges that indicate the point estimates could shift considerably with even a modestly different patient population.

Why does this matter beyond the pages of a biostatistics seminar? Because the original manuscript frames its three factors as candidates for individualized postoperative surveillance intensity, a recommendation that presumes a level of estimate stability that the underlying event count cannot yet support. In clinical practice, surveillance intensity translates into scan frequency, endoscopic monitoring, and the emotional and financial burden borne by patients. If a model flags a patient as high risk on the basis of an unstable hazard ratio, the resulting care pathway may be built on statistical sand. The commentary’s authors argue that the clinical implication is direct: the three-factor risk model should be validated in a cohort with complete staging data for all patients, reported with events-per-variable transparency, and stratified by the specific immune checkpoint inhibitor used before cycle count and treatment-to-surgery interval inform surveillance decisions for individual patients.

The cycle count variable receives particularly close scrutiny. It was identified as an independent predictor of reduced disease-free survival at three or more cycles, yet it pooled patients who received five different immune therapies administered on different schedules. Pembrolizumab and sintilimab are typically dosed on three-week cycles, while tislelizumab and camrelizumab regimens in Chinese clinical practice have used variable three- to four-week intervals depending on the accompanying chemotherapy backbone. The commentary illustrates the mismatch with simple arithmetic: a patient completing three cycles on a three-week schedule received roughly nine weeks of systemic drug exposure, while a patient completing two cycles on a four-week schedule received roughly eight weeks. Cycle count alone, in other words, does not consistently track cumulative treatment duration or drug exposure across this heterogeneous cohort, raising the possibility that the association is an artifact of grouping agents with different pharmacokinetic rhythms under a single ordinal number.

This operational ambiguity collides with the original study’s own biological interpretation. Zhang and colleagues proposed in their discussion that additional cycles may mark a biologically distinct subgroup of patients with a suboptimal early response to therapy, a hypothesis that makes the specific regimen and its dosing interval directly relevant to understanding what more than two cycles actually represents. Yet that operationalization was not addressed. Sengan and Ramaiah note that before cycle count is used to flag patients for closer surveillance, clarifying whether the association holds within each regimen subgroup, or instead reflects pooling artifacts, would meaningfully change how the variable should be applied at the bedside. Exposure-response literature in clinical pharmacology has repeatedly warned that time-to-event outcomes can be distorted when adaptive dosing schedules and heterogeneous agents are analyzed as if they were homogeneous exposures.

Despite the pointed critique, the commentary is not a rejection of the original work. Sengan and Ramaiah describe the study as a genuinely useful, single-institution account of a rapidly growing patient population, one whose honest acknowledgment of potential collider bias reflects appropriate caution rarely stated plainly in similar retrospective series. Their message is fundamentally constructive: the enthusiasm surrounding immunochemotherapy and the rising numbers of patients achieving pathological complete response deserve rigorous evidence, not fragile models. As immunotherapy reshapes the prognosis of esophageal squamous cell carcinoma, they conclude, the field’s statistical standards must evolve in step with its therapeutic optimism, ensuring that the tools used to individualize postoperative care stand on foundations solid enough to bear the weight of clinical decisions.

Subject of Research: Statistical validity of a prognostic risk model for esophageal squamous cell carcinoma patients achieving pathological complete response after neoadjuvant immunochemotherapy

Article Title: Comment on “Survival of esophageal squamous cell carcinoma achieving pathological complete response after neoadjuvant immunochemotherapy”

Article References: Sengan, S., & Ramaiah, S. (2026). Comment on “Survival of esophageal squamous cell carcinoma achieving pathological complete response after neoadjuvant immunochemotherapy”. Journal of Cancer Research and Clinical Oncology, 152(9), Article 174. https://doi.org/10.1007/s00432-026-06607-5

Image Credits: AI Generated

DOI: 10.1007/s00432-026-06607-5

Keywords: esophageal squamous cell carcinoma, pathological complete response, neoadjuvant immunochemotherapy, Cox regression, collider bias, disease-free survival, immune checkpoint inhibitors, surveillance, prognosis, biostatistics, esophageal cancer, immunotherapy