To explore the diagnostic features of large B-cell lymphoma of the serous cavity after chemotherapy for gastric cancer.

A retrospective analysis of a case with large B-cell lymphoma in the serous cavity that occurred after chemotherapy for gastric cancer in a patient admitted to Weifang People′s Hospital on January 1, 2023 was performed, including clinical and pathological data, combined with literature review, to summarize the diagnostic features.

The patient, a 71-year-old female, developed cough and phlegm 1.5 years after chemotherapy for gastric cancer, and chest tightness and dyspnea after activity. The patient underwent total gastrectomy plus regional lymph node dissection in September 2022, and the postoperative pathology showed poorly differentiated adenocarcinoma of whole stomach. The pathological stage was ypT4aN0Mx, and the tumor regression grade was 3. Chest CT showed a left pleural effusion. B lymphocyte gene rearrangement: monoclonal rearrangement of B cell receptors was observed. Lymphoma immunophenotyping (flow cytometry method): monoclonal B lymphocytes that were negative for CD5 and CD10, accounted for 11.4% of nucleated cells. According to the clinical data, morphological features, immunocytochemical stain results, gene rearrangement and flow cytometry, the pathological diagnosis was large B-cell lymphoma with pleural effusion as the main manifestation. 5.5 months after diagnosis, the patient still had pleural effusion as the main manifestation, without systemic lymph node enlargement.

Large B-cell lymphoma with pleural effusion diagnosed as the main manifestation after cancer chemotherapy should be distinguished. Pathologic and immunocytochemical stain features can be used to diagnose lymphoma cells in pleural effusion.