ESTRO 2024 - Abstract Book

S1500

Clinical - Lower GI

ESTRO 2024

We included consecutive LARC patients from a single health board if they underwent curative-intent NAT between start dates June 2016 – July 2021. CT images were obtained at the level of the third lumbar vertebrae as previously described (13). Semi-automated segmentation of images was performed by Hounsfield units (HU) as previously described (Figure 1) (14-16). The modified Glasgow Prognostic score (mGPS) was used a circulating SIR measurement and defined as previously described (17). Carcino-Embryonic Ag (CEA) was considered high >5ug/L, and neutrophil to lymphocyte (x10^9/l) ratio (NLR) was considered high >5.

Results:

303 patients met inclusion criteria. 66% of patients were male, median age 63.6. BMI did not differ significantly between genders ( p = 0.410 ). On analysis of changes to BCp between pre- and post-NAT scan dates, median measurements of all parameters decreased, but not significantly. 26.4% achieved a ‘complete response’ (pCR / sustained cCR). On analysis of BCp, a VF Area / SF Area ratio ≥0.4 associated with incomplete response (p=0.003). Univariate logistic regression analysis revealed mrT-stage ( p=0.002 ), mrEMVI ( p<0.001 ), VFA/SFA ratio ( p=0.003 ), and CEA >5 ( p=0.006 ) all predicted response. mrT-stage ( OR 2.10, 95%CI 1.11–3.97, p=0.022 ), mrEMVI ( OR 1.98, 95%CI 1.12–3.51, p=0.019 ), VFA / SFA ratio ≥0.4 ( OR 2.39, 95%CI 1.22–4.12, p=0.010 ), and CEA >5 ( OR 1.97, 95%CI 1.07–3.65, p=0.031 ) were independent predictors of incomplete response on multivariate analysis. A VFA/SFA ratio ≥0.4 significantly associated with male gender ( p<0.001 ), rising age category ( p<0.001 ), rising BMI ( p=0.011 ), and a higher Skeletal Muscle Index ( p<0.001 ). Raised mGPS ( p=0.026 ) and raised NLR ( p=0.029 ) (as markers of raised SIR) also associated with VFA/SFA ratio ≥0.4.

Conclusion:

This study performed automated measurements of BCp at pre- and post-NAT timepoints to explore potential markers of tumour response in LARC. This is the largest study to date that explores the relationship of BCp, SIR, and NAT response (7).