Cytologic effects of photodynamic therapy in body fluids

Photodynamic therapy (PDT) has been used in phase I clinical trials at the National Institutes of Health for the treatment of malignancies disseminated within the peritoneal and pleural cavities. Review of records revealed 18 patients who were treated with PDT between April 1988-June 1993. Sixty-five pleural and peritoneal fluids, 22 pre- and 43 post-PDT, were available for evaluation. Mesothelial cell changes seen post-PDT included: increased nuclear-to-cytoplasmic ratios in 7/18 (39%), cytomegaly in 9/18 (50%), and multinucleation in 12/18 (67%), with Touton-like giant cells in 3/18 (17%). Additional changes noted post-PDT comprised histiocytic aggregates in 9/18 patients (50%), with granuloma-like clusters in 3/18 (17%), acute and chronic inflammation in 13/18 (72%), and eosinophilia in 8/18 (44%). Residual tumor was present in 7/18 (39%) patients post-PDT. In 2 patients with malignant mesothelioma, benign mesothelial cells with cytologic changes post-PDT were difficult to distinguish from malignant cells. Mesothelial cell changes following PDT, specifically increased nuclear-to-cytoplasmic ratios and cytomegaly, should be recognized to avert false-positive diagnoses of tumor. In patients with malignant mesothelioma, and less commonly with adenocarcinoma, benign mesothelial cells with changes secondary to PDT may be difficult to distinguish from tumor cells.