Esophageal squamous cell carcinoma transformed into neuroendocrine carcinoma after neoadjuvant immunochemotherapy: A case report.

Immunotherapy provides durable responses for locally advanced esophageal carcinoma clinical therapy in numerous patients. However, the mechanisms of resistance to immunotherapy have not been elucidated. The phenomenon of the histological transformation of non-small cell lung cancer to small cell lung cancer resulting in resistance to immune checkpoint inhibitors (ICIs) has been reported. It remains unclear whether ICIs or chemotherapy could cause a similar transformation from esophageal squamous cell carcinoma (ESCC) to esophageal neuroendocrine carcinoma (ENEC). The present study report the case of a patient initially diagnosed with stage II ESCC who underwent radical surgery after three cycles of neoadjuvant therapy with cisplatin, albumin bound paclitaxel and ICIs. Immunohistochemical staining confirmed the absence of the SCC component and the presence of the NEC component, with negativity for CK5/6 and tumor protein p40, but positive expression of tumor protein p53, pan-cytokeratin, synaptophysin and CD56. The patient was followed up for 5 months with no treatment or postoperative complications. In conclusion, histological transformation to ENEC is a potential mechanism of acquired resistance to ICIs in ESCC. Prospective larger studies are warranted to further characterize ESCC-to-NEC transformation on use of ICIs.