eP689 - Proctectomy Alone vs. Proctectomy with Concomitant En-bloc Resection in Downsized T4b Rectal Cancer Following Total Neoadjuvant Therapy

Purpose/Background: Total neoadjuvant Treatment (TNT) is becoming more widely accepted due to its benefits, including increased complete response rates and better patient compliance with treatment. However, a concern arises with tumor fragmentation in the utilization of TNT. While the primary, visible tumor may be eradicated, there is a possibility that small clusters of viable tumor cells might remain scattered within the area formerly occupied by the tumor. As a result, proctectomy alone might lead to both local and distant recurrences in patients whose rectal cancer had previously invaded other organs or structures and then underwent downsizing. Therefore, our study aims to compare long-term oncological outcomes between patients treated with proctectomy alone and those treated with proctectomy with concomitant en-bloc resection. We hypothesize that proctectomy with concomitant en-bloc resection can provide enhanced long-term oncological outcomes.Methods/Interventions: We conducted a retrospective review of patients who completed the entire TNT regimen for locally advanced rectal cancer between 2015 and 2022. We included patients whose tumors initially had an organ or structure invasion (T4b) but subsequent downsizing to T4a or lower following TNT based on the MRI findings. Patients with persistent tumor invasion or who achieved a complete clinical response (cCR) were excluded. Our primary outcomes focused on local recurrence and distant metastasis rates. Proctectomy with concomitant en-bloc resection is defined as removing additional organs and structures initially invaded by the tumor, with TME in its entirety.Results/Outcomes: Of the 208 patients who completed the full TNT regimen, 39 (18.7%) had tumors that invaded an organ or structure. Among them, thirteen patients (33.4%) underwent surgery due to the downsized tumor, and were followed for a median duration of 32 months (16-37). Various organ and structural invasions were observed in the patients (prostate:4, bladder:4, seminal vesicle:3, levator muscle:3, vagina:1, cervix:1). Some patients had multiple invasions. The median age of these surgical patients was 64 years (48-66), with 3 (23.1%) being female. Proctectomy alone was performed for 8 (61.5%), while 5 (38.5%) underwent proctectomy with concomitant en-bloc resection. Histopathology revealed all margins were clear in 13 patients (100%). Throughout the study, there were no instances of local recurrence or mortality. However, one patient, whose initial levator muscle invasion had disappeared, developed lung metastasis eight months after undergoing standard TME. Thus, the 12-month survival rate of the proctectomy alone was 88%. All other patients remained disease-free, showing no local or distant recurrence.Conclusion/

Discussion: Proctectomy alone and proctectomy with concomitant en-bloc resection yield comparable long-term oncological outcomes in downsized T4b rectal cancer patients following TNT. Although the distant metastasis rate is lower after en-bloc resection, the modest sample size prevents us from drawing definitive conclusions.