1108 - Short-Term Radiotherapy plus Chemotherapy Increased the T Downstaging Rates Compared to Long-Term Chemoradiotherapy in Low-Lying Locally Advanced Rectal Cancer: A Post-Hoc Analysis of the STELLAR Trial
Presenter(s)
J. Lei1, Y. Tang2, N. Li3, W. Liu4, S. Chen5, S. Li6, Q. Xiao7, Y. LI3, and J. Jin7; 1National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College,Shenzhen,518116,China, Shenzhen, China, 2State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/ National Clinical Research Center for Cancer/ Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 3State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, 4Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, 5Department of Radiation Oncology, Fujian Medical University Union Hospital, Fujian Key Laboratory of Intelligent Imaging and Precision Radiotherapy for Tumors (Fujian Medical University), Fuzhou, China, 6Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education/Beijing), Department of Radiation Oncology, Peking University Cancer Hospital and Institute, Beijing, China, 7National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital and Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, Shenzhen, China
Purpose/Objective(s):
The STELLAR trial proved that preoperative short-term radiotherapy followed by chemotherapy (TNT) was not inferior to the long-term chemoradiotherapy (CRT) in patients with locally advanced rectal cancer (LARC). We aimed to determine whether TNT increased T downstaging rates in low-lying LARC than CRT.Materials/Methods:
In the STELLAR study, patients age 18-70 years,clinical primary tumor (cT) stage 3-4 and/or regional lymph node (N)–positivity without distant metastases, and rectal adenocarcinoma with tumor location in the distal and middle third of the rectum were randomly enrolled. Patients were assigned to TNT group or CRT group. The TNT group had short-term radiotherapy (25Gy/5fx) followed by four cycles of CAPOX. The CRT group had radiotherapy (50Gy/25fx) concurrently with capecitabine. Postoperative chemotherapy comprised two cycles of CAPOX in the TNT group or six cycles of CAPOX in the CRT group. We compared TNT to CRT in patients with tumors located <5 cm from the anal verge. T downstaging were defined as pathological (i.e. patients who achieved ypT stage less than cT stage), and clinical (i.e. patients who achieved a sustained cCR choosing watch and wait strategie). We compared categorical variables by chi-square test and continuous variables by Mann Whitney U or unpaired t-test. Univariate and multivariate binary logistic regressions were performed to investigate associations of baseline characteristics on achieving T downstaging. Statistical significance was defined as p-values = 0.050 and all tests were two-tailed.Results:
A total of 295 patients were low-lying LARC among 591 patients, of whom 147 allocated in TNT group and 148 in CRT group. Age, gender, ECOG status, cT, cN, mesorectal fascia (MRF) involvement, extramural vascular invasion (EMVI) were well balanced between groups. After neoadjuvant therapy, 112 patients in TNT group and 103 patients in CRT group received surgery, of whom 87(78%) and 72(70%) patients received abdominoperineal resection (APR) respectively. 101(90%) patients in TNT group and 85(83%) patients in CRT group achieved R0 resection. In TNT group, 85 patients (58%) achieved T downstaging (pathological:66, clinical:19), while 57 patients(39%) (pathological:46, clinical:11) achieved T downstaging in CRT group. Multivariate binary logistic regression revealed that TNT was associated with higher T downstaging rates (odds ratio 0.52, 95%CI 0.31-0.89), EMVI negative was associated with better T downstaging too(odds ratio 0.57, 95%CI 0.33-0.97). Besides, Patients who achieved T downstaging had a significantly lower rate of R1 resection (9% Vs 18%, p= 0.041) and better 3-year locoregional recurrence-free survival (95.1% Vs 81.4%, p=0.001), 3-year distant metastasis-free survival (86.3% Vs 63.6%, p=0.000), but didn't have difference in 3-year overall survival (87.6% Vs 86.5%, p=0.178).Conclusion:
TNT could achieve better T downstaging in low-lying LARC than CRT. Other characteristic associated with T downstaging was EMVI status.