LUDWIG, KIRK A.

105 Background: Patients with potentially resectable dMMR/MSI-H colon cancer (CC) often receive neoadjuvant immunotherapy (IO) if co-morbid conditions or the extent of disease preclude upfront surgery. We investigated the outcome of such patients treated in a real-world setting. Methods: This is a single-center retrospective study that included patients with dMMR/MSI-H localized and oligometastatic CC receiving neoadjuvant IO between January 1, 2016, and July 31, 2022 with a data cut-off date of September 15, 2022. Electronic charts were reviewed to gather data on patient characteristics, tumor characteristics, detailed treatment, toxicity, treatment response, and survival. The response was assessed by radiologic studies, endoscopy, pathology in resected patients, and circulating tumor DNA. Results: The study included 24 patients with a median age of 69 years (range, 32 to 91); 12 (50%) patients were female, and 5 (21%) patients were African American. Among the patients included, 12 (50%) had localized CC (9 of whom had clinical stage III disease), and the rest had oligometastatic CC. The reasons for not undergoing upfront surgery were co-morbidity in 12 patients (50%), disease extent in 11 (46%), and both in 1 (4%). Four patients (17%) received the ipilimumab/nivolumab combination, and the rest received pembrolizumab. Most patients (63%) received IO in the first-line setting. The median duration of IO and the time to best response were 7.5 months (range, 2 to 55) and 3 months (range, 3 to 12), respectively. Among 23 evaluable patients, the overall response rate (ORR) was 74 % (17/23), with complete response (CR) in 13 (57%), and partial response (PR) in 4 (17%) patients. Response assessment is pending in 1 patient. Four patients (17%) had stable disease (SD), and 2 patients (8 %) experienced progressive disease (PD) on IO (1 with localized and the other with metastatic CC). The median progression-free survival (PFS) and overall survival (OS) did not reach for the whole group after a median follow-up of 12.5 months (range, 2 to 69 months), with 19/24 (79 %) patients remaining progression-free. Three patients underwent surgery with 2/3 achieving pathological CR. Among the 12 patients with localized CC, ORR was 73% (6 CR, 2 PR, 2 SD, 1 PD, and 1 assessment pending); median PFS and OS were not reached after a median follow-up of 9 months (range, 2 to 45) with 1 patient experiencing progression on IO at the time of data cut-off. No unexpected toxicity was observed. Conclusions: In this small cohort of patients with dMMR/MSI-H localized and oligometastatic CC, most patients showed deep and durable responses to neoadjuvant IO, obviating the need for surgery. Progression on IO was rare. This real-world data support investigating a non-operative paradigm in patients with dMMR/MSI-H localized and oligometastatic CC.

TPS234 Background: Total neoadjuvant therapy (TNT) followed by total mesorectal excision (TME) is one of the standard treatment options for patients with locally advanced rectal cancer (LARC). A commonly employed TNT protocol consists of 8 biweekly cycles of oxaliplatin-based chemotherapy (CT) followed by radiation concurrent with fluoropyrimidine-based chemotherapy (CRT) for about 6 weeks. During the TNT, patients undergo tumor response assessments periodically with standard modalities (SM) consisting of pelvic magnetic resonance imaging (MRI) and proctoscopic/endoscopic examination. The objective of the current protocol is to evaluate the feasibility of tumor response assessment by ctDNA in patients with LARC undergoing TNT. The present feasibility study is designed to collect preliminary data to evaluate if a subsequent larger validation study is justified. If ctDNA-based response assessment is validated, ctDNA can potentially replace at least some components of the SM (for example, MRI) as tumor response assessment by SM is often time-consuming, expensive, and poses logistical challenges. Methods: Patients with LARC undergoing TNT will be enrolled. After obtaining informed consent, venous blood samples will be obtained for ctDNA level measurements at the following time points: baseline (within 1 week before the CT begins), after 4 cycles of CT within +/- 5 days of the MRI study, after 8 cycles of CT within +/- 5 days of the MRI study, and 1 to 14 days before TME. ctDNA levels will be measured by a commercially available ctDNA assay (Signatera by Natera), and ctDNA response is defined as >90% drop in the ctDNA level after treatment compared to the baseline level. Tumor response will be evaluated after 4 and 8 cycles of CT by SM. Primary endpoint: correlation between the response rate (RR) assessed by ctDNA and by SM after 4 cycles of CT. Secondary endpoints: 1) correlation between the RR assessed by ctDNA and by SM after 8 cycles of CT, and 2) correlation between the ctDNA defined RR and the complete pathological response (pCR) rate. The trial will enroll 30 patients. To evaluate the primary endpoint, differences in ctDNA levels between the baseline and 4-cycles post-CT will be computed. The differences will then be expressed as a proportion of each patient’s baseline level, D. This relative change, D, will be compared between the responder and non-responder groups using a two-sample Welch’s t-test. Similar methods will be applied for the secondary endpoints. All analyses will use the nominal type I error level of 0.05 and two-sided tests. Clinical trial information: NCT04670588.

44 Background: Despite an alarming rise in incidence, data on survival outcome and treatment response of young-onset (age < 50 years) locally advanced rectal cancer (YO-LARC) patients receiving total neoadjuvant therapy (TNT) are sparse. We retrospectively compared the outcome between YO-LARC and later-onset (aged 50 years or older) LARC (LO-LARC) patients treated with TNT. Methods: After the institutional review board approval, electronic medical records of the LARC (T3/T4 or node-positive) patients treated with TNT at a tertiary care cancer center between January 1, 2015, and June 30, 2020, were reviewed for data collection. TNT consisted of systemic chemotherapy with oxaliplatin-based regimens for 16 weeks followed by long-course radiation with concurrent capecitabine or 5-fluorouracil (CRT). Patients receiving only preoperative CRT were excluded. Most patients underwent surgical resection following the TNT. Non-operative management was offered to patients if TNT resulted in clinical complete response (cCR). The following comparisons between the YO-LARC and the LO-LARC patients were performed: patient characteristics, pathological complete response (pCR) rate, combined pCR + cCR rate, disease-free survival (DFS), and overall survival (OS). Results: Of 72 patients included in the analysis, 44(61%) were male, 49 (68%) were Caucasian, and 62 (86%) had clinical stage III disease. The study included 26 (36%) patients with YO-LARC (median age, 43 years) and 46 (64%) patients with LO-LARC (median age, 64 years). The comparison of patient characteristics that included gender, clinical stage, baseline carcinoembryonic antigen level, the distance of the tumor from the anal verge, presence of high-risk features, and histologic grade did not differ significantly between the groups. There were no statistically significant differences in pCR and combined pCR+cCR rates (p = 0.16) between the groups: YO-LARC, 12 % (3/26) and 15 % (4/26), respectively; LO-LARC, 22% (10/46) and 30% (14/46), respectively. Either group did not reach median DFS and OS after a median follow-up of 38 months for survivors. The estimated 5-year OS rates in patients with YO-LARC and LO-LARC were 86 % (95% confidence interval [CI], 69% to 100%) and 84% (95% CI, 68% to 100%), respectively (p = 0.92). The estimated 3-year DFS rates in patients with YO-LARC and LO-LARC were 67 % (95% CI, 50% to 89%) and 83% (95% CI, 72% to 95%), respectively (p = 0.19). Conclusions: The current retrospective analysis did not demonstrate significant differences in the pCR rates, combined pCR +cCR rates, DFS, or OS between the YO-LARC and LO-LARC patients treated with TNT.

AbstractBackgroundA pooled post hoc responder analysis was performed to assess the clinical benefit of alvimopan, a peripherally acting mu‐opioid receptor (PAM‐OR) antagonist, for the management of postoperative ileus after bowel resection.MethodsAdult patients who underwent laparotomy for bowel resection scheduled for opioid‐based intravenous patient‐controlled analgesia received oral alvimopan or placebo preoperatively and twice daily postoperatively until hospital discharge or for 7 postoperative days. The proportion of responders and numbers needed to treat (NNT) were examined on postoperative days (POD) 3–8 for GI‐2 recovery (first bowel movement, toleration of solid food) and hospital discharge order (DCO) written.ResultsAlvimopan significantly increased the proportion of patients with GI‐2 recovery and DCO written by each POD (P < 0.001 for all). More patients who received alvimopan achieved GI‐2 recovery on or before POD 5 (alvimopan, 80%; placebo, 66%) and DCO written before POD 7 (alvimopan, 87%; placebo, 72%), with corresponding NNTs equal to 7.ConclusionsOn each POD analyzed, alvimopan significantly increased the proportion of patients who achieved GI‐2 recovery and DCO written versus placebo and was associated with relatively low NNTs. The results of these analyses provide additional characterization and support for the overall clinical benefit of alvimopan in patients undergoing bowel resection.