Metastatic seminomas in lymph nodes: CD10 immunoreactivity can be a pitfall of differential diagnosis.

Metastatic seminoma can potentially be confused with lymphoma in a lymph node biopsy. Here, we report a case in which the immunohistochemistry of CD10 was a pitfall in the differential diagnosis of a metastatic seminoma, and further present a brief study of CD10 expression in a seminoma series. A 67-year-old man, who had a history of lobectomy of the lung due to squamous cell carcinoma 2 years prior, showed lymphadenopathy of the neck and the paraaorta on follow-up study by fluorodeoxyglucose-positron emission computer tomography scan. The biopsy of the cervical node demonstrated infiltration of large atypical cells. The results of the screening immunohistochemistry were CD20(-), CD3(-), CD10(+), CD30(-), AE1/AE3(-), and placental alkaline phosphatase(-), providing the impression of CD10-positive lymphoma. However, the following studies revealed germ cell characteristics [OCT3/4(+), SALL4(+), and CLDN6(+)], confirming the diagnosis of seminoma. We further evaluated CD10 expression in a series of seminomas (n=16). Strong positivity was observed in 14 cases; partial and weak positivity, in 2 cases. These findings should be considered in the differential diagnosis of seminoma.