Muscle, not BMI, carried the survival signal in head and neck radiotherapy

Design

Single-centre retrospective cohort with automated CT body composition analysis

Population

1187 patients having definitive radiotherapy for head and neck cancer, 659 with imaging analysis

Primary outcome

Overall survival

Effect

Skeletal muscle HR 0.67 (95% CI 0.50 to 0.89); intermuscular fat HR 1.28 (1.03 to 1.58)

This single-centre retrospective cohort included 1187 patients receiving definitive radiotherapy for head and neck cancer between 2014 and 2024. In 659 of them, an automated deep-learning tool measured muscle and fat compartments on the planning CT.

Higher BMI was associated with better overall survival (overweight HR 0.70, 95% CI 0.56 to 0.89; obesity HR 0.67, 0.50 to 0.89). But the extra mass in higher BMI was mostly subcutaneous fat. In the imaging group, more skeletal muscle was associated with better survival (HR 0.67, 0.50 to 0.89), while more fat between muscles was associated with higher mortality (HR 1.28, 1.03 to 1.58).

This supports looking past BMI at body composition before treatment, and the planning CT already holds the information. The associations are observational and confounded by disease stage, swallowing and nutrition. The practical step is early dietetic and swallowing support for patients with low muscle mass, which matters especially where undernutrition is common at presentation, as in many Indian head and neck cancer clinics.

• Assess nutrition and muscle mass before head and neck radiotherapy, not BMI alone.
• Refer patients with weight loss or low muscle mass to dietetics before treatment starts.
• Arrange early speech and swallowing therapy to help preserve oral intake.
• Encourage resistance exercise where the patient is able, to maintain muscle during treatment.

Why it matters

A reassuring BMI can hide low muscle mass, so the patients most at risk may not look it.

Don't overread it

This retrospective cohort shows association only; it does not show that building muscle improves survival.

The statistics, in plain English

A hazard ratio of 0.67 for higher muscle means about a third lower risk of death over follow-up, but this is an association. Patients with more muscle are often fitter, less advanced and eating better, so muscle may be a marker of these rather than a cause of survival.

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