Abstract: Objective: A case of lymphoma with the first manifestation of pleural effusion was reported to provide a reference for the
diagnosis and treatment of effusion lymphoma. Methods: Pleural effusion was collected to make cell blocks, which routinely stained
with HE, immunohistochemical staining（IHC）and in situ hybridization（ISH）detection were performed to observe tissue morphology
and evaluate immunophenotype. We followed up the patient subsequently. Results: A lot of atypical lymphoid cells were found in
pleural effusion. The results of IHC staining showed as follows: CD20, PAX5, BCL-2, BCL-6 and MUM1 were positive, while the
CD45RO, Calretintin, CD10, CD3, CK20, CK7, C-MYC and HHV-8 were negative; Ki-67 positive index was 80%. In situ
hybridization showed that the tumor cells nuclei were negative for EBER. The patient was diagnosed as diffuse large B-cell lymphoma
with secondary exudation and non-germinal central type（Non-GCB）. The patient deteriorated and died two months after diagnosis.
Conclusion: Effusion lymphoma is a rare type of lymphoma. Once malignant effusion in serous cavity occurs in patients with
lymphoma, the prognosis is poor. This disease should be differentiated from inflammatory exudation and metastatic tumors, and IHC is
useful for the diagnosis.

Key words: effusion lymphoma, primary and secondary, clinical diagnosis and treatment