Primary Objective:~-To estimate the median progression-free survival (PFS) (from the start of adjuvant pembrolizumab until locoregional progression, development of distant metastatic disease, or death) in stage IVB ATC patients with gross disease, treated with external beam radiation (+/- concomitant chemotherapy) followed by adjuvant pembrolizumab. Patients will be patients enrolled from cohort 1 and 2 (cohort 1: >51 Gy; cohort 2: <50 Gy).~Secondary Objective:~-To estimate median overall survival in stage IVB ATC patients treated with external beam radiation (+/- concurrent chemotherapy) followed by adjuvant pembrolizumab. Patients will be stratified by dose of external beam radiation.~Exploratory Objective:~-To estimate the median disease-free survival (DFS) in patients with stage IVB ATC treated with surgery/external beam radiation/concomitant chemotherapy followed by adjuvant pembrolizumab (cohort 3).
This is an open label, single center, phase 2 trial of adjuvant pembrolizumab after external beam radiation to the primary tumor in patients with stage IVB (disease localized to the neck) ATC. This drug trial will estimate the median progression-free survival (PFS) (from the start of adjuvant pembrolizumab until locoregional progression, development of distant metastatic disease, or death) in stage IVB ATC patients with gross disease, treated with external beam radiation (+/- concomitant chemotherapy) followed by adjuvant pembrolizumab. Patients will be patients enrolled from cohort 1 and 2 (cohort 1: >51 Gy; cohort 2: <50 Gy).