A 67-year-old woman was admitted to our hospital because of fever. Chest roentgenogram showed an enlargement of mediastinal lymph nodes. Despited thorough examination, no definite diagnosis could be made. The mediastinal lymph nodes got smaller over the next 3 weeks and a chest roentgenogramtaken 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.

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... ic examination of pretracheal lymph node specimens showed invasion of poorly differentiated adenocarcinoma associated with abundant tumor-infiltrating lymphocytes. The other lymphnodes showed sarcoid reaction. Although she has been followed for one year and 11 months, no primarysite of the cancer has been found. Metastasis of cancerof unknown origin to mediastinal lymph nodes is extremely rare. It is also interesting that thelymph node swelling diminished spontaneously. The tumor-infiltrating lymphocytes and sarcoid reactions may have been immunological responsesto the cancer and may have caused the transient regression.