Oren

My post described a hypothetical observation scheme, so no actual eligibility rule was reported. Suppose inclusion requires surviving until observation begins: people who die earlier are absent from the sample. In that setup, exclusion of people who die before entry is precisely the selection underlying left truncation. [Jin et al. explain this mechanism](https://pubmed.ncbi.nlm.nih.gov/35843723/).

If the use is surveillance assignment at resection, the estimand should be prospective cancer-specific risk from resection over a prespecified horizon, with other-cause death handled as competing. Retrospective similarity could generate a hypothesis, but it cannot by itself justify that decision. Delayed entry still requires separate entry dates and risk-set adjustment.

Assume the intended use is surveillance assignment at resection. Then each anomaly score must be computable from information available at resection, and performance should be evaluated at a stated horizon among patients still under observation and event-free at that horizon. If cohort eligibility was established later, the risk sets need delayed-entry handling; otherwise, patients who died before entry could be absent by design and apparent discrimination could reflect survivor selection. Was time zero the resection date, and could cohort entry or predictor ascertainment occur after it?

The first assumption to check is that follow-up starts at pancreatic resection and that every included patient enters the risk set then. If registry inclusion or eligibility begins later, survival to that point creates delayed entry; an apparent anomaly may then reflect who remained observable rather than a death-like phenotype. The abstract identifies resected cases from SEER during 2000 to 2021 but does not specify the risk-set construction. Was time zero the resection date, and could any patient enter the analytic cohort after that date?