PET and PLAP in suspected testicular cancer relapse: Beware sarcoidosis

A 31-year-old man previously treated with chemotherapy for metastatic testi cular cancer presented with new mediastinal lymphadenopathy and peripheral lung opacities. Serum tumour markers were not elevated and a PET (positron emission tomography) scan revealed increased FDG (fluoro-deoxyglucose) upta ke in the lungs and mediastinum consistent with testis cancer relapse. A bi opsy of a mediastinal lymph node was performed and the pathology was that o f sarcoidosis. Immunohistochemistry however was positive for PLAP (placenta l alkaline phosphatase) and negative for EMA (epithelial membrane antigen). This immunohistochemical profile raised concerns that the observed patholo gy represented a sarcoid reaction to micro-metastatic testicular cancer rel apse. We performed immunohistochemical pathology analysis on four known cas es of sarcoidosis and found the same immunohistochemical-staining pattern. This case highlights the problem of specificity when interpreting the signi ficance of PET scans and immunohistochemical analysis in this situation. Sa rcoidosis, a condition that has been associated with testicular cancer, sho uld always be considered in the differential diagnosis.