Primary colorectal diffuse large B-cell lymphoma initially presenting with pleural effusion: report of one case and review of literature.

Gastrointestinal (GI) diffuse large B-cell lymphoma (DLBCL) is one of the frequently reported histologic subtypes of non-Hodgkin lymphoma (NHL) that occur in the GI tract. However, the presentation of quite different clinical manifestations, morphologic characteristics, immunophenotypes, and molecular biologic features is challenging for its diagnosis. Herein, we describe a rare case of primary colorectal DLBCL that occurred in a 59-year-old immunocompetent Chinese female who attended our respiratory clinic for the third time with an asymptomatic pleural effusion and pleural thickening. In her clinical setting, there was no history of trauma or travel, and no evidence of infections, connective tissue diseases, or malignancies such as pleural mesothelioma. Lymphoma was highly suspected for the enlargement of systemic lymph nodes and the multiple polypoid appearance in the rectum found by endoscopy examination. In a repeated colonoscopy, immunohistochemical and molecular features of the multiple "polyps" allowed diagnosis of colorectal diffuse large B-cell NHL. To our knowledge, this is the first case of a verified diagnosis of pleural effusion associated with a primary colorectal DLBCL. The purpose of this report is to alert clinicians that when we evaluate the causes of unexplained pleural effusion, lymphoma should be considered, particularly when the available examination data cannot be corroborated by clinical manifestations.