Objective: To investigate the clinical manifestations, pathological features, immunophenotype and diffe-rential diagnosis of pulmonary microcystic fibromyxoma(MFM). Methods: The clinical manifestations, histopathological features, and immunophenotype were analyzed retrospectively in a patient diagnosed as pulmonary MFM, and the related literature was reviewed. Results: A 63-year-old man was detected to have lung nodule located in upper left lobe by routine X-ray examination. The chest CT showed multiple nodules in different sizes and the largest one located in the upper left lobe with smooth borders and mild enhancement. The resection of left upper lobe in lung was performed for the patient. Grossly,the big tumor located close to the edge of the lobe and the size was about 1.5 cm×1.1 cm×0.7 cm. It was grayish red, soft and had relatively clear border. Microscopically, the tumor had clear edge, and extensive microcapsule structures were observed. The cell showed the shapes of spindle or stellate without cellular atypia or mitotic figures. The tissue had a lot myxoid stroma, abundant small blood vessels and scattered lymphocytes, plasma cells,mast cells and macrophages. The other small tumor (maximum diameter of 0.2 cm) with similar morphology was 0.2 cm away from the larger one. Its' immunophenotype showed that the tumor cells were diffuse vimentin positive, and Ki-67 labelling index was low(<1%). The immunohistochemical markers for epithelial cells, muscle cells, nerve cells, neuroendocrine cells, vascular endothelial cells, and mesothelial cells were all negative. The chromosome translocation was not observed in EWSR1 gene by fluorescence in situ hybridization. The chest CT scans of the patient were repeated 12 and 18 months post the surgery and showed the number and size of multiple small nodules in right lung increased slightly. Conclusions: Pulmonary MFM is a rare mesenchymal tumor, and histologic structure is characterized with presence of microcapsule and myxoid stroma, and the tumor cells were vimentin positive. The diagnosis of pulmonary MFM depends on the morphologic observation and immunohistochemical staining. So far, the recurrence or metastasis has not been reportedyet, however, the imaging follow-up of this case shows the nodules slightly increased in numbers and size, which suggests that pulmonary MFM may have malignant potential.
