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.