Clinical and Local Immune Factors Associated With Pleurodesis Outcomes in Breast Cancer Patients With Malignant Pleural Effusion: A Retrospective Study

Background Refractory malignant pleural effusion impairs activities of daily living in patients with advanced cancer, and pleurodesis is used to palliate dyspnea. However, factors associated with pleural effusion reaccumulation after pleurodesis in breast cancer remain insufficiently defined. We explored clinicopathological factors and selected local pleural immune responses associated with pleural fluid control after pleurodesis. Methods We retrospectively included 34 patients with advanced or recurrent breast cancer who underwent pleurodesis for malignant pleural effusion during 2015-2025. Patients were classified according to the presence or absence of documented pleural effusion reaccumulation after pleurodesis, irrespective of whether repeat drainage was subsequently performed. Associations between clinicopathological factors and reaccumulation were evaluated. Immunohistochemistry for MPO, a neutrophil marker, and CD206, an M2-like macrophage marker, was performed on available pleural effusion cell blocks. Results Of the 34 patients, 23 (68%) had no documented reaccumulation and 11 (32%) had reaccumulation. Hormone receptor positivity was more frequent in the non-reaccumulation group ( P = .045), which also showed trends towards longer disease-free interval and time to malignant pleural effusion. No clear differences were observed in systemic inflammatory markers. Immunohistochemistry showed trends towards more MPO-positive cells and fewer CD206-positive cells in the non-reaccumulation group, although neither difference was statistically significant. Conclusions Pleural fluid control after pleurodesis may be related to the clinical disease course of breast cancer. Opposite directional trends in MPO- and CD206-positive cells raise a hypothesis regarding the potential role of local inflammatory and immunoregulatory processes. These exploratory findings warrant further investigation.