Lymph node cancer of the mediastinal or hilar region with an unknown primary site

We herein report three cases of lymph node cancer of the mediastinal or hilar region, in which the primary sites could not be determined in spite of performing various systemic examinations. Two cases revealed a large cell anaplastic carcinoma in the mediastinal lymph node, while the other demonstrated a small cell carcinoma in the hilar lymph node. However, based on radiographic and pathological examinations, the primary sites could not be found in either the head and neck, lung, or abdominal organs. All cases underwent surgical resections for lymph node cancer, while two patients also received adjuvant therapy. Two patients experienced recurrence soon after treatment. Despite the rarity of this disease, lymph node cancer must always be kept in mind when an enlargement of either the mediastinal or hilar lymph node is detected in patients with an unknown primary site, and a poor prognosis is generally expected.