ESTRO 2024 - Abstract Book

S1560

Clinical - Lower GI

ESTRO 2024

treatment groups, to quantify the effect. The selected covariates considered as confounders for both propensity score analyses were: age, sex, clinical T-stage, clinical N-stage, metastases stage prior treatment and tumor differentiation. The balance of propensity-matched groups was assessed and confirmed via absolute value of the standardized differences less or equal than 0.1 being considered acceptable. Logistic and Cox regression analyses were performed and Kaplan Meier estimator was used for graphical representation and validation of the Cox model for survival outcomes. For all the statistical analysis, a two-sided p-value of less than 0.05 was considered significant.

Results:

The median follow-up of patients (165 male and 92 female) was 57 months (95%CI 54-60 months), the overall pCR rate was 26% (95%CI 20-32%). The 5-year LPFS, DFS and OS were 93% (95%CI 90-97%), 67% (95%CI: 61-74%) and 83% (95%CI 78-88%), respectively. The overall acute toxicity information was available in 153 patients. The acute toxicity greater and equal than 3 was 33% (51/153, 95%CI: 26-41%). No patients had acute grade 4 or 5 toxicity. In matched cohort with full method, pCR was significantly higher in patients treated with "high" CEM43 (p=0.01). Patients with "low" CEM43 had pCR rate of 11% (11/96, 95%CI: 7-19%) and "high" CEM43 of 28% (21/76, 95%CI: 19 39%). Similar results were obtained also in matched cohort using nearest neighbour method, the "low" and "high" CEM43 patient groups had significantly different pCR rates of 11% (8/70, 95%CI: 6-20%) and 27% (19/70, 95%CI: 18-38%), respectively (p=0.04). After full matching, potential prognostic factors were evaluated for pCR and survival outcomes. The uni- and multi-variable logistic regression analyses in full matched cohort showed that pCR was significantly associated with "high" CEM43, lymph node involvement and differentiation grade of the tumor (see Figure 1), indicating that a higher median thermal dose improved pCR (OR: 1.2; 95%CI: 1.1-1.3), the involvement of the lymph nodes impaired pCR (OR: 1.3; 95%CI: 1.1-1.6) and a reduced odds of moderately or poorly differentiated tumor is associated with pCR (OR: 0.7; 95%CI: 0.5-0.9). The same result was confirmed in the nearest matched cohort, reaffirming the association between "high" CEM43 and pCR. No significant difference was observed between "low" and "high" CEM43 groups in full matched cohort for 5-year DFS, LPFS and OS (Figure 2).

Conclusion:

High CEM43 (CEM43≥ 3.5 min) was associated with significantly higher pCR rate for LARC patients treated with neoadjuvant CRT+HT. This combined treatment approach should be investigated in prospective clinical trials including the organ preservation strategy.