A phase II study of induction PD-1 blockade in subjects with locally advanced mismatch repair-deficient rectal adenocarcinoma.

Abstract

TPS4123 Background: The treatment of patients with locally advanced rectal cancer includes total neoadjuvant therapy with chemotherapy, chemoradiation followed by surgery. While most rectal cancers respond to combination induction chemotherapy, patients with mismatch repair deficient (dMMR) or MSI-H tumors have a significantly higher chance of progression with this treatment regimen. dMMR or MSI-H tumors have shown remarkable responses to PD-1 blockade, but the effect of neoadjuvant checkpoint inhibition has not been well studied. In this trial we will determine the pathologic complete response rate (pCR) of neoadjuvant anti-PD-1 blockade followed by standard chemoradiation in dMMR or MSI-H locally advanced rectal cancer. We hypothesize that treatment naïve dMMR or MSI-H rectal cancers will achieve a robust clinical response to PD-1 blockade and that the total neodjuvant therapy with PD-1 blockade followed by chemoradiation will improve pCR rates. Methods: Eligible patients ≥18 years of age with Stage II (T3-4, N-) or Stage III (any T, N+) histologically confirmed dMMR or MSI-H (by NGS) rectal adenocarcinoma will be enrolled. Patients will receive TSR-042 (500mg IV) every 3 weeks for a maximum of 8 cycles (6 months of treatment). Imaging, internal endoscopic exam and ctDNA blood draw will be performed at 6 weeks and every 3 months during induction anti-PD-1 treatment. Adverse events and surgical complications will be graded according to the NCI CTCAE v5 and the Clavien-Dindo classification, respectively. Following neoadjuvant checkpoint blockade, patients will undergo conventional chemoradiotherapy followed by surgical resection. The primary endpoint is pathologic complete response compared with historical control in pMMR patients. Patients will be followed up every 6 months for assessment of disease-free survival for up to five years. Clinical trial information: NCT04165772 .