# Dose chemotherapy by muscle mass, not body surface area

Source: https://onco.cc/ideas/idea-bio2-lean-mass-dosing/  
OnCo record `idea-bio2-lean-mass-dosing` (Idea). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Chemotherapy doses are calculated from height and weight, a formula from the 1950s. Doses based on actual muscle mass may cause fewer severe side-effects.

## Summary

Body surface area poorly predicts clearance for most cytotoxics, and low lean body mass is associated with markedly higher rates of severe toxicity at standard doses, above all with fluoropyrimidines and taxanes. Lean mass is now measurable automatically from routine imaging, making an alternative dosing metric practical for the first time.

## Fields

- Kind: Idea
- Last checked: 2026-09-08
- Hypothesis: Lean-mass-based dosing reduces grade 3 or higher toxicity by a third compared with body surface area dosing, without reducing dose intensity delivered per unit of lean tissue or compromising efficacy.
- Rationale: Drug clearance tracks metabolically active tissue rather than total body size, which explains why sarcopenic patients are effectively overdosed. Pharmacogenomic dose adjustment for DPYD has already established that toxicity-driven dose individualisation is acceptable to clinicians and regulators.
- Proposed test: A randomised trial in one regimen with a high toxicity rate, comparing lean-mass dosing with standard dosing; primary endpoint severe toxicity, with pharmacokinetic sampling to confirm the mechanism.
- Maturity: speculative
- Actor: clinic

## Sources

- Bottleneck evidence (Cachexia, toxicity and the limits of the patient): Fearon et al., Definition and classification of cancer cachexia (Lancet Oncology 2011): https://doi.org/10.1016/S1470-2045(10)70218-7

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [HR-positive / HER2-negative breast cancer](https://onco.cc/cancers/breast-hr-positive/)
- technologies: [AI in radiology](https://onco.cc/technologies/radiology-ai-screening/), [CT (computed tomography)](https://onco.cc/technologies/ct/), [Cytotoxic chemotherapy](https://onco.cc/technologies/cytotoxic-chemotherapy/)
- drugs: [Capecitabine + temozolomide (CAPTEM)](https://onco.cc/drugs/capecitabine-temozolomide/), [Docetaxel](https://onco.cc/drugs/docetaxel/), [Paclitaxel / nab-paclitaxel](https://onco.cc/drugs/paclitaxel/)
- bottlenecks: [Cachexia, toxicity and the limits of the patient](https://onco.cc/bottlenecks/b-cachexia-supportive/), [Toxicity and quality of life are undervalued](https://onco.cc/bottlenecks/b-toxicity-qol/), [Wrong doses](https://onco.cc/bottlenecks/b-dose-optimisation/)
- key papers: [Definition and classification of cancer cachexia: an international consensus](https://onco.cc/key-papers/paper-fearon-lancet-oncol/)
- terms: [Sarcopenia](https://onco.cc/terms/sarcopenia/)
- roadmaps: [Chemotherapy roadmap: mustard gas → curative combinations → the warhead inside smarter drugs](https://onco.cc/roadmaps/chemotherapy-roadmap/)

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