Study of Durvalumab (MEDI4736) After Chemo-Radiation for Microsatellite Stable Stage II-IV Rectal Cancer

The FR-2 study is designed as a phase II, open label, single arm study in patients with microsatellite stable (MSS) stages II-IV rectal cancer, to assess the activity of PD-L1 inhibition with durvalumab (MEDI4736) monotherapy after standard chemo-radiotherapy (chemoRT). The study's primary aim is to determine the safety and efficacy of durvalumab immediately following chemoRT in patients undergoing subsequent surgery with stage II-IV rectal cancer. One dose of durvalumab will be given every 2 weeks for four total doses beginning within 3-7 days of completing chemoRT. Surgery for all patients must occur within 8-12 weeks of the final dose of RT. Adjuvant chemotherapy after surgical recovery is at the discretion of the treating physician. During a safety run-in, the first 6 patients will be closely followed for 30 days after last dose of durvalumab without further accrual of patients. Patients will receive durvalumab (750mg IV infusion once every 2 weeks) for 4 total doses. No other concurrent anti-neoplastic medications or treatments aside from standard supportive care will be allowed during the durvalumab treatment phase. The safety run-in portion of the study will proceed to full enrollment at the proposed study therapy dose, (750 mg IV infusion every 2 weeks), if one or less dose-limiting toxicity (DLT) or significant safety concern attributable to durvalumab is identified during the observation period of the first 6 patients. If there are two or more DLTs, accrual to the study will stop with reassessment of the protocol. A total of 44 patients will be enrolled in this study for a sample size of 41 surgically evaluable patients. Required tissue and blood samples will be collected at specific time points and submitted for correlative science studies. Optional tumor and blood samples will be collected from consenting patients upon disease recurrence or progression. Given the increasing use of non-operative therapy for patients with rectal cancer who achieve a complete clinical response and in order to maximize the inclusion of patients participating in this trial, the primary endpoint was changed from NAR score to modified NAR score (mNAR). The mNAR score substitutes values from clinical staging for the pathologic T-Stage and N-Stage for those patients who don't go to surgery because of a complete clinical response and consequently have no pathology. Additionally, because of enrollment challenges related to COVID-19 pandemic and the exploratory nature of including stage IV patients, the stage IV analysis was moved to exploratory and reducing the number of patients needing to be enrolled in the study to approximately 44.