Solitary Lung Metastasis of Prostate Cancer with a Long Disease-Free Interval and Normal Prostate-Specific Antigen Level

An 83-year-old man with core needle biopsy-proven Gleason score 5 prostate cancer had received radiotherapy including 18 Gy brachytherapy to the prostate cancer, leading to no locoregional and distant recurrence for more than 5 years with the normalization of elevated prostate-specific antigen (PSA) level before the radiotherapy. Due to the enlargement of coexisting ground glass nodule (GGN) in the left lung from 1 to 2.1 cm, the patient underwent wide resection of the GGN 7 years later. Under the diagnosis of adenocarcinoma in situ of the lung, follow-up computed tomography 6 months after the wide resection showed a rapid enlargement of a solid nodule having been judged as a presumed inflammatory nodule in the middle lobe, highly suggesting a malignant neoplasm of the lung. Due to both the tall columnar atypical cells with trabecular pattern on frozen section and no elevation of serum PSA level, we judged the nodule as a primary adenocarcinoma of the lung and further resected the middle lobe with lymph node dissection. Immunostaining of the tumor showed all the CK7, CK20, TTF-1, napsin A, synaptophysin, chromogranin, CD56, CDX2, p53, beta-catenin, and MUC2 negative, and PSA highly positive, clearly showing the solid nodule as a solitary lung metastasis of the prostate cancer. Physicians should note the possible solitary lung metastasis of prostate cancer, especially bearing indolent biology, with no elevation of the PSA level even after the completion of standard 5-year follow-up.