[Metastasis of an adenocarcinoma of unknown origin to mediastinal lymph nodes, and transient regression].

A 67-year-old woman was admitted to our hospital because of fever. Chest roentgenogram showed an enlargement of mediastinal lymph nodes. Despite thorough examination, no definite diagnosis could be made. The mediastinal lymph nodes got smaller over the next 3 weeks and a chest roentgenogram taken 4 months later showed no mediastinal lymphadenopathy. The mediastinal lymphadenopathy and fever recurred 5 months later. She underwent thoracotomy and the mediastinal lymph nodes were excised. Microscopic examination of pretracheal lymph node specimens showed invasion of poorly differentiated adenocarcinoma associated with abundant tumor-infiltrating lymphocytes. The other lymph nodes showed sarcoid reaction. Although she has been followed for one year and 11 months, no primary site of the cancer has been found. Metastasis of cancer of unknown origin to mediastinal lymph nodes is extremely rare. It is also interesting that the lymph node swelling diminished spontaneously. The tumor-infiltrating lymphocytes and sarcoid reactions may have been immunological responses to the cancer and may have caused the transient regression.