{
  "abstract": "BackgroundConversion surgery for stage IV gastric cancer is supported by a pooled overall survival hazard ratio of 0.36 (95% confidence interval 0.32-0.40) and, in the largest international cohort, median survival of 36.7 versus 12.5-13.8 months on chemotherapy. Survival is measured from diagnosis; the median diagnosis-to-gastrectomy interval is 124 days, which patients must survive to be counted surgical.\n\nMethodsWe simulated cohorts of 3,177 stage IV gastric cancer patients from published parameters: background median survival 14.5 months; median diagnosis-to-surgery interval 124 days (category-specific 92-174 days). Surgery had no effect (true hazard ratio 1.00 by construction). Data were analysed as the literature analyses them (exposure fixed at baseline, follow-up from diagnosis), and by time-varying Cox and landmark analysis. Confounding by indication was added in a second scenario.\n\nResultsUnder immortal time bias alone the naive analysis returned a hazard ratio of 0.794 (95% simulation interval 0.743-0.851), median survival 16.8 versus 12.8 months. Time-varying Cox recovered 1.000 and landmark analysis 1.000-1.004. Bias scaled with the interval: 0.849 at 92 days, 0.715 at 174 days. Adding confounding, the naive estimate fell to 0.601 (0.560-0.644) at strength 0.5 and 0.356 (0.323-0.385) at strength 1.5, overlapping the published estimate; median survival 21.9 versus 8.7 months. Correcting immortal time alone left residual bias (hazard ratio 0.439).\n\nConclusionsThe reported survival advantage of conversion surgery is reproducible where the operation does nothing; published estimates cannot distinguish benefit from bias. Resolving this requires individual patient data analysed with methods that assign person-time correctly, or completion of JCOG2301.",
  "abstract_shown": true,
  "affiliations": [
    "Ruijin Hospital, Shanghai Jiaotong University School of Medicine"
  ],
  "article_type": "PUBLISHAHEADOFPRINT",
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "B. K. Sah"
    },
    {
      "name": "C. Li"
    },
    {
      "name": "J. Li"
    },
    {
      "name": "Z. Zhu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/3b8jp09mvqfqx.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.09.01.26361986",
  "fulltext_url": "https://www.medrxiv.org/content/10.64898/2026.09.01.26361986v1.full",
  "id": "3b8jp09mvqfqx",
  "issns": [],
  "landing_url": "https://www.medrxiv.org/content/10.64898/2026.09.01.26361986v1",
  "language": null,
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "medrxiv",
      "gastroenterology"
    ],
    [
      "openalex",
      "2740|Gastric Cancer Management and Outcomes"
    ]
  ],
  "openalex": "W7208756805",
  "pdf_url": "https://www.medrxiv.org/content/10.64898/2026.09.01.26361986v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-01",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/3b8jp09mvqfqx.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:39Z",
      "native_id": "10.64898/2026.09.01.26361986",
      "source": "medrxiv",
      "url": "https://www.medrxiv.org/content/10.64898/2026.09.01.26361986v1"
    }
  ],
  "subjects": [
    {
      "field": "medicine",
      "origin": "medrxiv:gastroenterology",
      "subfield": "general"
    }
  ],
  "title": "Immortal time bias reproduces the reported survival benefit of conversion surgery in stage IV gastric cancer: a simulation study",
  "title_text": "Immortal time bias reproduces the reported survival benefit of conversion surgery in stage IV gastric cancer: a simulation study",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:39Z",
  "url": "https://research.draconitic.com/paper/3b8jp09mvqfqx",
  "venue": "medRxiv",
  "versions": []
}