Concurrent CD5-negative small lymphocytic lymphoma (SLL) and CD5-positive metastatic carcinoma of unknown primary in a lymph node biopsy

CD5 expression is considered a key marker for the diagnosis of chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL). We report an unusual case of CD5-negative (CD5-) SLL with a concurrent CD5-positive (CD5+) adenocarcinoma of unknown primary involving the same lymph node. An 83-year-old woman with a history of CD5- B cell lymphoma diagnosed on a core biopsy of a cervical lymph node presented with jaundice and was found to have a 2. 5-cm pancreatic mass. A fine needle aspiration of the mass revealed a CD5- monotypic B cell population. A subsequent excisional biopsy of a cervical lymph node showed morphologic findings typical for SLL, including the presence of multiple proliferation centers. However, the neoplastic lymphocytes were negative for CD5 by both flow cytometric analysis and immunohistochemistry. Interestingly, multifocal metastatic adenocarcinoma was identified and was positive for CD5. Lack of CD5 expression often leads to the exclusion of CLL/SLL, particularly in small biopsy samples. However, rare cases of CD5- CLL/SLL have been reported. In addition, CD5 is not an exclusive marker for lymphoid cells; its expression has been observed in several non-hematopoietic neoplasms. This report briefly reviewed and discussed CD5- CLL/SLL and CD5+ carcinoma reported in the literature.