eP229 - Case Series on Perioperative Immune Checkpoint Inhibition in Locally Advanced Rectal Adenocarcinoma at Mayo Clinic

Purpose/Background: Studies have shown the effectiveness of immune checkpoint inhibition (ICI) in patients with tumors demonstrating microsatellite instability (MSI-H) and an associated defect in DNA mismatch repair (dMMR). In particular, KEYNOTE-177 and CHECKMATE-142 demonstrated significant survival benefit for patients with unresectable or metastatic colorectal cancer with MSI-H or dMMR. Recently published case reports and series have demonstrated similar outcomes for patients with locally advanced and resectable rectal cancer. Here, we report on the treatment regimens, surgical outcomes and complications of 6 patients treated with perioperative ICI across the Mayo Clinic enterprise.Methods/Interventions: A database search of locally advanced dMMR patients who received perioperative ICI was conducted and limited to patients within the Mayo Clinic electronic medical record and across the Mayo Clinic enterprise since 2015. Patients with prior line treatment and/or surgical resection were included as well as those who did not receive prior treatment. De novo locally advanced and locally recurrent disease were also included. Patient chart review was conducted and pertinent data points including: patient demographics, disease status/involvement, treatment regimen, dates, surgical procedures and disease response. Radiographic response was determined by RECIST criteria. Pathological response was collected. Post-operative outcomes including: length of stay and surgical complications were also collected.Results/Outcomes: 6 patients with Stage III rectal adenocarcinoma were identified to have received perioperative ICI. Treatment regimens were widely variable. ICI regimens included the use of pembrolizumab or nivolumab + ipilimumab. 1 patient had upfront resection followed by disease recurrence within 6 months and then received ICI. 3 patients received a neoadjuvant ICI including: ICI + concurrent RT, ICI + RT, Chemo + ICI. 2 Patients received neoadjuvant and adjuvant ICI. Number of ICI cycles prior to surgery ranged from 2 to 49. Grade 3 or higher immune-related adverse events occurred in 2 patients.
Surgical procedures included open low anterior resection (LAR), pelvic exenteration and proctocolectomy and laparoscopic proctectomy. Length of stay ranged from 3 to 12 days. 3 patients were readmitted within 30 days of procedure (2 infection, 1 DVT).
Of the 6 patients, 4 patients achieved either a pathological complete response, 1 patient had a radiographic partial response, 1 patient continues to have radiographic stable disease.Conclusion/

Discussion: Patients included in this study represent a wide variation in treatment regimens and complications. Ultimately their outcomes show significant response to disease. Further, larger studies are required to determine the optimal treatment regimen.