# Crossover in trials

Source: https://onco.cc/terms/crossover/  
OnCo record `crossover` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

When patients in a trial's control arm are allowed to switch to the experimental drug after their cancer progresses. It is fair to patients but blurs the survival comparison, because the control group has now had the drug too.

## Summary

Crossover is common in trials of drugs already approved elsewhere or clearly active (imatinib in GIST, osimertinib in FLAURA, 177Lu-PSMA in VISION and PSMAfore, where 84% of controls crossed over) and explains why such trials often show large progression-free survival gains but little or no overall survival difference. Statistical corrections (rank-preserving structural failure time, inverse probability of censoring weighting) estimate what survival would have been without crossover but rely on assumptions and are treated cautiously by regulators, who may still demand an OS trend. In regulatory debates, crossover cuts both ways: it can hide a true survival benefit or excuse its absence.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: cross-over; crossover-adjusted; crossover adjustment; adjusted for crossover; permitted crossover; crossover was permitted; crossover rate; post-progression therapy; subsequent therapy; subsequent treatment; RPSFT; rank-preserving structural failure time; IPCW; treatment switching; unplanned crossover; confounded by crossover

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Crossover_study
- Wikipedia: https://en.wikipedia.org/wiki/Crossover_study

## Connected records

- terms: [Clinical equipoise](https://onco.cc/terms/clinical-equipoise/), [Control arm and comparator (investigator's choice)](https://onco.cc/terms/control-arm/), [Estimands and intercurrent events (ICH E9(R1))](https://onco.cc/terms/estimand/), [Hazard ratio (HR)](https://onco.cc/terms/hazard-ratio/), [Kaplan-Meier curve, censoring and proportional hazards](https://onco.cc/terms/kaplan-meier-curve/), [N-of-1 trial](https://onco.cc/terms/n-of-1-trial/), [Overall survival (OS)](https://onco.cc/terms/os/), [Progression-free survival (PFS)](https://onco.cc/terms/pfs/), [Surrogate endpoint](https://onco.cc/terms/surrogate-endpoint/), [Surrogate endpoint validation: which stand-ins have earned trust](https://onco.cc/terms/surrogate-validation/), [Why trials fail: underpowered, wrong endpoint, control arm drift, subgroup fishing, crossover](https://onco.cc/terms/trial-failure-modes/)
- fronts: [Drug Discovery Platforms](https://onco.cc/fronts/drug-discovery/)
- trials: [ClarIDHy](https://onco.cc/trials/claridhy/), [CodeBreaK 200](https://onco.cc/trials/codebreak-200/), [PSMAfore](https://onco.cc/trials/psmafore/), [TheraP (ANZUP 1603)](https://onco.cc/trials/therap/), [VISION](https://onco.cc/trials/vision/)
- cancers: [Prostate cancer](https://onco.cc/cancers/prostate/)
- drugs: [Idecabtagene vicleucel](https://onco.cc/drugs/idecabtagene-vicleucel/), [Ivosidenib](https://onco.cc/drugs/ivosidenib/)

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JSON: https://onco.cc/api/v1/entities/crossover.json