# Backbone, add-on and monotherapy

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

## TL;DR

Trial-design vocabulary: the backbone is the established treatment everyone in the trial receives; the add-on is the new drug tested on top of it; monotherapy means the drug alone. Most modern approvals are add-ons to a backbone.

## Summary

Testing a new drug added to standard therapy (backbone) versus the backbone alone is the fastest route to approval because it needs no head-to-head against the standard, but it means patients receive more drugs and more toxicity, and it can obscure whether the new agent could replace rather than supplement (the 'chemotherapy-free' question in CLL, lung cancer and myeloma). Single-agent activity in early trials (objective response rate as monotherapy) is the usual evidence that a drug contributes. Regulators sometimes require 'contribution of components' studies when a combination is approved without it.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: backbone; chemotherapy backbone; backbone therapy; add-on; add-on therapy; monotherapy; single agent; single-agent; single-agent activity; combination partner; chemotherapy backbones; single agents

## Sources

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

## Connected records

- terms: [Control arm and comparator (investigator's choice)](https://onco.cc/terms/control-arm/), [De-escalation, escalation and response-adapted therapy](https://onco.cc/terms/de-escalation/), [Doublet, triplet and quadruplet regimens](https://onco.cc/terms/doublet-triplet/), [Objective response rate (ORR)](https://onco.cc/terms/orr/)
- fronts: [Chemotherapy](https://onco.cc/fronts/chemotherapy/)

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JSON: https://onco.cc/api/v1/entities/backbone-add-on.json