AUTHOR=Zhang Mai , Yang Hua , Chen Ling , Du Kunli , Zhao Lina , Wei Lichun 

TITLE=Pathological complete response in MMR-deficient/MSI-high and KRAS-mutant patient with locally advanced rectal cancer after neoadjuvant chemoradiation with immunotherapy: A case report

JOURNAL=Frontiers in Oncology

VOLUME=Volume 12 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2022.926480

DOI=10.3389/fonc.2022.926480

ISSN=2234-943X

ABSTRACT=Till date, preoperative chemoradiation (CRT) is the standard of care for patients with locally advanced rectal cancer(LARC) regardless of status of MMR. Immunotherapy showed promising results in the neoadjuvant treatment trials in patients with mismatch repair-deficient (dMMR) or high microsatellite instability (MSI-H) LARC. The efficacy of CRT plus PD-1 inhibitor in these patients with complex gene mutation remains unclear. Additionally, very few studies were reported on whether such combination could induce abscopal effect. We report a case of dMMR and MSI-H LARC with KRAS mutation achieved pathological complete response of primary lesion and liver metastases after neoadjuvant short-course radiotherapy followed by 4 cycles chemotherapy of XELOX plus PD-1 inhibitor tislelizumab and a subsequent total mesorectal excision. This case indicates that this combined treatment strategy has remarkable clinical response both in locoregional and distant diseases, which potentially leads to reduce the risk of distant metastases and better locoregional control for this subgroup of population.