ESTRO 2024 - Abstract Book

S1470

Clinical - Lower GI

ESTRO 2024

One patient received chemotherapy before the start of neoadjuvant radiotherapy. All 26 patients underwent NA RT using VMAT and received concurrent chemotherapy of oral administration of S1 during NA-RT. Of the 26 patients, two, and one patient(s) failed to complete radiotherapy due to grade 3 diarrhea, and grade 3 depression, respectively. Twenty-one patients underwent radical surgery after radiotherapy 10 (range, 9-34) weeks after the completion of radiotherapy. One, one and three patient(s), was considered unresectable in the primary tumor after NA-RT, received systemic chemotherapy without primary surgery due to lung metastasis which was observed after NA-RT, and selected watch-and-wait approach after total neoadjuvant therapy, respectively. Complete resection was achieved in all 21 patients. Pathological response of grade 0, 1a, 1b, 2 and 3 (complete response) were observed in 0 (0.0%), 7 (33.3%), 4 (19.0%), 8 (38.1%) and 2 (9.5%) patients, respectively [1]. A patient of three undergoing watch-and-wait approach developed local progression and received salvage surgery 12 months after NA-RT. Grade 2 non-hematological toxicities included dermatitis, diarrhea and anal pain in two (7.7%), two (7.7%) and three (11.5%) patients, respectively. Grade 3 non-hematological toxicities included diarrhea and enterocolitis in three (11.5%) and two (7.7%) patients, respectively. In addition, hematological toxicities included grade 2 leukopenia in two (7.7%) patients and grade 4 thrombocytopenia in one (3.8%) patient. In the median follow-up term of 14 (range, 3-27) months, three (11.5%), five (19.2%), and one (3.8%) patients developed local failures, distant failures, and died, respectively. The 2-year LC, progression-free survival (PFS), and overall survival (OS) rates were 82.9%, 75.3% and 94.7%, respectively.

Conclusion:

NA-RT using VMAT combined with oral administration of S-1 showed acceptable acute adverse event rates and pathological response rates. The OS, PFS and LC after neoadjuvant radiotherapy for rectal cancer in the present study were consistent with those described previously. In the future, this prospective study should include a larger number of patients with a longer follow-up.