Radiotherapy for cytokeratin-positive interstitial reticulum cell (CIRC) tumor on epicardium: a case report

Cytokeratin-positive interstitial reticulum cell (CIRC) tumor is an extremely rare malignant neoplasm and a subtype of fibroblastic reticular cell tumor, classified within the dendritic cell tumor group. We describe a case of an epicardial CIRC tumor that was resected and subsequently recurred in the left pulmonary hilum. This recurrence was treated with immunotherapy followed by radiotherapy. A 71-year-old man with a history of colon cancer incidentally had a mass bordering the epicardium on a postoperative follow-up computed tomography scan. Pericardial tumor resection was performed due to suspected metastasis from colon cancer. Histopathologically, the patient was diagnosed as a CIRC tumor (programmed death ligand 1 expression rate > 95%). Seven months after pericardial surgery, the patient was treated with nivolumab because of local recurrence in the left pulmonary hilum, but the tumor size gradually increased. Three months after the initiation of nivolumab, the patient had a completely atelectatic left lung due to tumor invasion into the left main bronchus and was treated with external beam radiotherapy of 66 Gy in 33 fractions. One and a half months after the completion of radiotherapy, the atelectasis disappeared, and aeration was greatly improved. Three months after the completion of radiotherapy, atelectasis and pericardial effusion appeared owing to tumor regrowth, and the patient died of heart failure 2 months later. This report provides insights into the efficacy of immunotherapy and radiotherapy for CIRC tumor.