Utilisation of intramuscular and intermuscular fat to develop a new skeletal muscle grading score which can predict treatment outcomes for locally advanced rectal cancer.

Overall complete response (oCR) was achieved in 25.7% of patients in this retrospective cohort of locally advanced rectal cancer patients.

• Retrospective analysis performed on 226 patients with localised rectal adenocarcinoma
• Patients were treated at Western Health between 2013 and 2024
• oCR was defined as pathological complete response or sustained clinical complete response for at least 3 years
• 25.7% of the total cohort achieved oCR

oCR was significantly associated with lower MRI T stage, increased age at diagnosis, and a better SMS, while active smoking decreased oCR in multivariable analysis.

• Multivariable analysis identified lower MRI T stage as a significant predictor of oCR
• Increased age at diagnosis was positively associated with oCR
• Higher SMS score was positively associated with oCR
• Active smoking was negatively associated with oCR in multivariable analysis

The Skeletal Muscle Score (SMS) demonstrated a strong gradient in oCR rates, ranging from 0% for SMS of zero to 60% for SMS of four.

• SMS was developed as a scored scale from 0 to 4
• Patients with an SMS of zero had a 0% oCR rate
• Patients with an SMS of four had an oCR rate of 60%
• The score was developed to predict overall complete response

A novel Skeletal Muscle Score (SMS) was developed using AI-derived body composition metrics including skeletal muscle and intramuscular/intermuscular adipose tissue (IMAT) measurements.

• Body composition metrics including SM and IMAT volume and density were extracted from the L1-S5 vertebral region
• Measurements were extracted using validated AI software enabling 3D body composition analysis
• The SMS was scored on a scale of 0 to 4
• The score utilised both skeletal muscle (SM) and intermuscular/intramuscular adipose tissue (IMAT) parameters

Higher SMS correlated with improved overall survival, cancer-specific survival, and disease-free survival.

• Secondary outcomes included overall survival, cancer-specific survival, and disease-free survival
• A higher SMS was associated with improved outcomes across all three survival endpoints
• The SMS provided prognostic information beyond treatment response alone

The SMS scoring system is proposed as a tool for individualised risk stratification to enhance patient counselling in rectal cancer.

• The SMS is described as a 'novel, AI-derived body composition assessment'
• The scoring system 'could provide clinicians with individualised risk stratification to enhance patient counselling'
• The study supports increasing evidence that adipose tissue parameters, in addition to sarcopenia measures, have an important role in rectal cancer outcomes
• AI advances allowing 3D body composition analysis of IMAT from CT scans underpinned the development of this score