# Control arm and comparator (investigator's choice)

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

## TL;DR

The group in a randomised trial that gets the existing standard treatment, against which the new drug is judged. Whether the control is the true current standard, an outdated one, or a menu of options chosen by each doctor ('investigator's choice') changes how much a positive result means.

## Summary

The comparator should be the best available treatment at the time; trials using a weaker control (chemotherapy alone when chemo-immunotherapy was standard, or a suboptimal dose) draw regulatory and ODAC criticism and may not translate into practice. Investigator's or physician's choice from a list of chemotherapies is common in later-line trials (ASCENT, DESTINY-Breast04, TROPiCS-02) and is realistic but heterogeneous. Head-to-head trials of two new agents are rare and mostly sponsored by challengers (MARIPOSA vs osimertinib, HARMONi-2 ivonescimab vs pembrolizumab). Placebo or observation controls are used where no active standard exists, as in adjuvant and maintenance settings.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: control arm; control group; comparator; comparator arm; active comparator; active control; standard arm; standard-of-care arm; investigator's choice; investigator choice; physician's choice; treatment of physician's choice; TPC; chemotherapy of choice; versus chemotherapy; vs chemotherapy; experimental arm; treatment arm; head-to-head; head to head; control arms; comparators

## Sources

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

## Connected records

- terms: [Backbone, add-on and monotherapy](https://onco.cc/terms/backbone-add-on/), [Blinding (double-blind, open-label, placebo-controlled)](https://onco.cc/terms/double-blind/), [Clinical equipoise](https://onco.cc/terms/clinical-equipoise/), [Crossover in trials](https://onco.cc/terms/crossover/), [Declaration of Helsinki](https://onco.cc/terms/declaration-of-helsinki/), [External and synthetic control arms](https://onco.cc/terms/external-control-arm/), [Intention-to-treat (ITT) and per-protocol analysis](https://onco.cc/terms/intention-to-treat/), [Non-inferiority trial](https://onco.cc/terms/non-inferiority/), [Pragmatic trial](https://onco.cc/terms/pragmatic-trial/), [Standard of care](https://onco.cc/terms/standard-of-care/), [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: [ACT IV](https://onco.cc/trials/act-iv/), [CONVERT](https://onco.cc/trials/convert/), [DESTINY-Breast04](https://onco.cc/trials/destiny-breast04/), [KEYNOTE-024 & KEYNOTE-189](https://onco.cc/trials/keynote-024-189/)

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JSON: https://onco.cc/api/v1/entities/control-arm.json