Abstract
Cytokeratin (CK) is a specific marker of adenocarcinoma. However, cases of CK7-positive esophageal squamous cell carcinoma (ESCC) have only rarely been reported. We herein report a case of unresectable CK7-positive ESCC with aggressive liver metastasis following nivolumab treatment initiation. Nivolumab treatment was discontinued after one course because of complications. Notably, the liver metastases exhibited accelerated growth. Immunostaining of the necropsy specimens revealed diffuse positivity for forkhead box protein A1 (FOXA1)/CK7, thus indicating a potent poor immune response. The potential correlation between CK7 expression and the immune checkpoint inhibitor response may offer valuable insights into the development of effective therapeutic strategies.