Metastatic hepatocellular carcinoma with CD138 positivity: an unusual mimic of multiple myeloma?

CD138 is a monoclonal anti-syndecan-1 antibody that is often used to identify plasma cells in the bone marrow of patients with multiple myeloma (MM). Several carcinomas may also express CD138 including prostate, colon, renal cell, and hepatocellular carcinoma (HCC). We report a case of metastatic HCC that presented as a soft tissue mass on the back of a 67-year-old male. Based on the clinical and radiologic findings, MM was strongly suspected. In addition, fine-needle aspiration biopsy (FNAB) of the mass revealed neoplastic cells that were positive for CD138, both by immunohistochemistry (IHC) and flow cytometry. The cytomorphologic features however did not support a diagnosis of MM, but were consistent with metastatic HCC. Our case highlights the potential problems that may arise by over-reliance on IHC and flow cytometry. Careful morphologic assessment as well as clinical and radiologic correlation are very important when evaluating any CD138-positive neoplasm. This approach should improve diagnostic accuracy and reduce the risk of erroneous interpretation of aberrant IHC results. In addition, we examined the expression of CD138 in known cases of HCC.