Primary unknown cancer in pulmonary hilar lymph node with spontaneous transient regression: Report of a case

69-year-old man was referred to our hospital in December 1993 because an abnormal mass had been detected in the right pulmonary hilum. Computed tomography (CT) of the chest revealed a swollen hilar lymph node between the right middle and lower lobe bronchi, and an adherent tumor in the right ventrobasal segment (S8). Chest roentgenogram in February 1994, however, showed no evident tumor in the right lung field. In March 1996, the mass in the right pulmonary hilum reappeared on chest roentgenogram. Chest CT revealed a swollen hilar lymph node between the right middle and lower lobe bronchi, but there was no tumor in right S8. The patient underwent video-assisted thoracoscopy on 17 May 1996. Intraoperative needle biopsy of the node revealed cancer cells. We performed right middle and lower bilobectomy with mediastinal dissection. Histological diagnosis revealed a large cell carcinoma almost completely occupying a hilar lymph node. The resected middle and lower robes showed no tumors, except for a coagulation necrosis measuring 1.5 cm in diameter in S8b, corresponding to the site where a tumor shadow had been depicted on the CT image in December 1993. We concluded that the coagulation necrosis might have been the primary site of the tumor, which had spontaneously regressed and then appeared in the metastatic interlobar node.