Poster Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2026

Body composition changes during neoadjuvant treatment for locally advanced rectal cancer predicts pathological tumour response. (139998)

Alex Besson 1 2 , Ke Cao 1 , Josephine Yeung 1 , Fiona Reid 1 3 , Peter Gibbs 4 5 , Justin Yeung 1 3
  1. Department of Surery, University of Melbourne, Parkville, VIC, Australia
  2. Melbourne Academic Centre of Health, North Melbourne, VIC, Australia
  3. Colorectal Surgery, Western Health, Footscray, VIC, Australia
  4. Medical Oncology, Western Health, Sunshine, VIC, Australia
  5. Walter and Eliza Hall Institute, Parkville, VIC, Australia

Background

Total neoadjuvant therapy (TNT) has become the standard of care for locally advanced rectal cancer (LARC) and has increased pathological complete response (pCR) rates when compared to chemoradiotherapy alone. Sarcopenia is associated with poor oncological outcomes; however, the prognostic role of dynamic body composition changes during neoadjuvant therapy remains underexplored. This study aimed to assess whether CT-derived body composition changes that occur during neoadjuvant therapy predict pCR in LARC patients.

 

Methods

A retrospective cohort study of 111 patients (2013-2024) with LARC was conducted at Western Health. Skeletal muscle (SM), intramuscular adipose tissue, visceral adipose tissue and subcutaneous adipose tissue volume and density was quantified from diagnostic and restaging CT scans using a validated AI segmentation model. Changes in body composition during neoadjuvant treatment were analysed to determine to the impact on pCR.

 

Results

Increased SM volume, ≥3.0% for males and ≥2.4% for females, was associated with higher pCR rates (34.1% vs 9.5%, p=0.006), which persisted in patients treated with TNT. An increase in SM density ≥3.8% for males and ≥26.6% for females predicted pCR (38.5% vs 15%, p=0.019). Multivariable analysis identified a change in SM volume (OR 9.62, 95% CI 1.86-49.6, p=0.007) and density (OR 4.00, 95% CI 1.10-14.3, p=0.036) above the sex specific threshold to be strongly associated with pCR.

 

Conclusion

An increase in SM volume and density during neoadjuvant therapy has a strong positive association with complete pathological response in LARC patients.