ESTRO 2024 - Abstract Book

S1557

Clinical - Lower GI

ESTRO 2024

Vanessa Di Cataldo 1 , Viola Salvestrini 1 , Giulio Frosini 1 , Lucia Angelini 1 , Niccolò Bertini 1 , Marco Banini 1 , Cinzia Talamonti 2 , Lorenzo Livi 1 1 Radiation Oncology, Azienda Ospedaliero Universitaria Careggi, Università di Firenze, Firenze, Italy. 2 Medical Physics Unit, AOU Careggi, Firenze, Italy

Purpose/Objective:

Neoadjuvant radiotherapy (NRT), both delivered as short course (SCRT) or long course with concomitant capecitabine (LCCRT), has gained prominence as an essential component of the multimodal treatment approach for locally advanced rectal cancer (LARC). NRT has demonstrated improved local control and facilitated sphincter preserving surgery, leading to better patient outcomes [ 1 ; 2 ]. Pathologic complete response (pCR) has emerged as a valuable prognostic marker for overall survival (OS) in RC patients . Patients achieving pCR have shown a significantly better prognosis and improved survival rates, thus becoming a critical endpoint in assessing treatment response [ 3 ; 4 ]. Ongoing research endeavors seek to identify factors that may influence pCR attainment in rectal cancer patients, including treatment-related timing [ 5 ; 6 ; 7 ; 8 ]. To date, radiation-surgery interval (RSI) up to 10 weeks is the most widely accepted to balance tumor response to NRT and risk of surgical complications [ 9 ]; however, it is unclear whether a longer waiting interval would lead to further tumor downstaging and/or a higher rate of pCR. In this retrospective series, we aimed to study the predictive value of pCR on OS and the potential effect of RSI on pCR in LARC patients treated with NRT.

Material/Methods:

Clinical and treatment-related data from patients with LARC undergoing NRT with LCCRT or SCRT at our Institution between January 2019 and March 2023 were retrospectively collected. Survival analysis was performed using the Kaplan Meier method; log-rank test was used for curve comparison. Categorical and continuous variables were assessed using the χ 2 -test and Kruskall-Wallis test: multiple regression was performed on variables that proved statistically significant (p<0.05).

Results:

Overall, 125 patients were analyzed. Median age at diagnosis was 72 years (IQR 62-75) and 87 patients (70%) were male. Thirty-three patients (26%) were diagnosed with clinical T4 and 52 (42%) with clinical N2 lymph node involvement. Mesorectal fascia (MRF) and extramural venous invasion (EMVI) were reported in 24 and 19 cases respectively (19 and 15%). Eighty-eight patients (70%) underwent LCCRT, while 37 (30%) patients received SCRT. Nine patients (7%) had induction chemotherapy (CT) before NRT. All patients underwent surgery; median RSI was 9 weeks (IQR 7-11 weeks) and pCR was achieved in 27 cases (22%). At a median follow up of 23 months (range 3 51 months), 13 patients had died (10%). Median OS was 47 months (95% CI 40-47). Survival rates at 2 years and 3 years were 93.5% and 87%, respectively. Among the variables analyzed (age, sex, lymph-nodal involvement, cTstage, induction CT, MRF and EMVI involvement, RT schedule, pCR) at univariate analysis, only pCR was correlated with improved OS (median not reached versus 40 months, p= 0,021) [ Fig.1 ]. Median interval between neoadjuvant treatment and surgery did not significantly differ between patients with and without pCR (10 versus 9 weeks, NS). Lower rates of pCR were correlated with use of SCRT (10% versus 27%, p=0.041) and cT4 stage at diagnosis (3% versus 27%, p=0.0083). None of the other variables analyzed were statistically associated with pCR.