Primary atypical carcinoid tumor of the mediastinum: a very rare finding

Primary neuroendocrine tumors (NETs) of the mediastinum are very rare. Prognosis is usually poor despite treatment options. We present the case of a primary atypical carcinoid tumor of the mediastinum successfully treated by multimodal approach. A 50-year-old man presented for asthenia, dyspnea, and substernal sense of weight for two weeks. A chest-CT scan revealed a tumor mass of 107×55×95 mm³ localized in the anterosuperior mediastinum compressing both brachiocephalic veins, the superior vena cava, the pericardium, and lungs. A FDG-PET demonstrated high FDG uptake only in the mediastinal mass; no metastases were seen. CT-guided needle biopsy revealed a NET; cells were immunoreactive for synaptophysin; Ki67 was 20%. After neoadjuvant chemotherapy, the chest CT-scan showed a significant reduction of the tumor. A surgical excision was proposed. The tumor was radically removed along with a partial resection of the vena cava and reconstruction with a bovine pericardium patch. The patient underwent 25 sessions of adjuvant radiotherapy. Microscopically the tumor showed clusters of medium-sized cells, eosinophilic cytoplasm with nuclear pleomorphism and small nucleoli, arranged in trabeculae, nests and lobules. No thymic tissue was found. Immunohistochemically the tumor cells were positive for CD117, synaptophysin, chromogranin, CD56, cytokeratin pool, epithelial membrane antigen (EMA), and negative for thyroid transcription factor-1 (TTF1), leukocyte common antigen (LCA), fibroblast-activation protein (FAP), prostate-specific antigen (PSA), P63, CD5 and CD99. Mitoses were found to be 8/10 HPF. The Ki67 was 10%. A diagnosis of primary NET of the mediastinum, intermediate grade (G2), atypical carcinoid according to WHO 2015, was formulated. Even in case of primary NE mediastinal tumor, a multimodal approach could lead to long-term survival.