Rapid tumor progression complicated with liver abscess in a patient with gastric cancer receiving nivolumab therapy.

Immune checkpoint inhibitors have been approved for treating various cancer types. However, several studies reported rapid tumor progression, a condition known as hyperprogressive disease, after treatment with immune checkpoint inhibitors. We present the case of a 73-year-old man diagnosed with recurrent gastric cancer with liver and lymph node metastases detected in the presence of obstructive jaundice. Concomitant administration of nivolumab with cytotoxic chemotherapy as first-line chemotherapy effectively controlled the tumor. Nevertheless, once cytotoxic chemotherapy was discontinued and nivolumab monotherapy was initiated to treat liver abscess complications, the tumor rapidly progressed, ultimately leading to the patient's death. This is the first report on rapid tumor growth observed during subsequent treatment with nivolumab after initial antitumor effects were confirmed. This case report describes the possibility of rapid tumor growth in patients receiving immune checkpoint inhibitor therapy, including in cases where this therapy showed antitumor efficacy in the initial therapeutic evaluation. Therefore, patients receiving immune checkpoint inhibitor therapy need to be monitored.