Trial of Chemoradiation and Pembrolizumab in Patients With Rectal Cancer

This is a phase II, prospective open label multi-center study in which subjects with stage II-III rectal cancer will be accrued in order to determine the pathological complete response rate of neoadjuvant pembrolizumab in combination with chemoradiation treatment (CRT). Subjects must have a diagnosis of rectal cancer, stage II (T3-4, N0) or stage III (any T, N1-2). Subjects must have received no prior treatments (chemotherapy, pelvic radiation or surgery) for their rectal cancer. Eligible subjects will receive standard chemoradiation with pembrolizumab administered every 3 weeks on days 1, 22, and 43 of the neoadjuvant interval. In all subjects, restaging endorectal or pelvic MRI with chest and abdominal CT will be performed at 6-8 weeks after completion of neoadjuvant treatment to determine resectability and to rule out any evidence of metastases. Subjects who have resectable disease will undergo surgery within 2-4 weeks of imaging; 8-12 weeks after completion of chemoradiation. Subjects who are found to have unresectable or metastatic disease post treatment with the combination of CRT+ pembrolizumab should receive standard of care definitive treatment per the discretion of their treating physician.