Extracavitary/solid variant of primary effusion lymphoma presenting as a gastric mass

Primary effusion lymphoma (PEL) is a rare subtype of large B-cell lymphoma associated with human herpesvirus 8 (HHV8). It has the highest incidence in HIV-positive individuals. It often presents as a malignant pleural, peritoneal and/or pericardial effusion without a detectable solid mass. Most cases are co-infected with Epstein-Barr virus (EBV). Rare cases of HHV8-positive lymphoma with features similar to PEL can present as tumor masses and are considered to represent an extracavitary or solid variant of PEL. We report a case of EBV negative, extracavitary/solid variant of primary effusion lymphoma presenting as a gastric mass.

A 48-year-old man was admitted to an outside hospital with abdominal pain and weight loss. At the outside hospital, he was found to be HIV positive and have a 3 × 2 cm gastric mass. He was subsequently diagnosed with ALK negative anaplastic large cell lymphoma by gastric biopsy. The patient was referred to Harbor-UCLA Medical Center for further management. Review of the outside slides and additional stains performed at our hospital revealed sheets of large anaplastic lymphoma cells that were positive for CD30, CD138, MUM1 and HHV8, focally weakly positive for CD3, and negative for other T- and B-cell markers and EBER, consistent with extracavitary/solid variant of primary effusion lymphoma. Interestingly, for the first time, cyclin D1 positivity was also demonstrated in PEL.

Primary effusion lymphoma, particularly the extracavitary/solid variant, is very rare, and the diagnosis can be challenging. In some cases, when CD30 is uniformly positive, this lymphoma can be misdiagnosed as ALK negative anaplastic large cell lymphoma. This lymphoma can also aberrantly express T-cell markers as seen in this case, making diagnosis even more difficult. Awareness of the existence and the features of solid variant PEL and assessment for HHV8 infection are essential for correct diagnosis.