[Solitary fibrous pseudopapillary tumor of the lung: pulmonary fibroadenoma and adenofibroma revisited].

We describe a peculiar pulmonary lesion, that we interpreted as a pseudopapillary variant of solitary fibrous tumor. The patient was a 62-year-old asymptomatic male, non smoking, presenting with a peripheral nodule, 0.8 cm across, located in the lower lobe of the right lung. The patient is alive and well 18 months after surgical excision of the nodule. Microscopically, the lesion was well-circumscribed and characterized by a diffuse pseudopapillary pattern. Pseudopapillae were large, and were covered by a rim of cubic epithelium devoid of atypia. The stromal axis was fibrous and contained scattered bland spindle cells. Immunohistochemically, the latter were strongly positive for vimentin and CD34, focally positive for BCL2 and CD99, negative for cytokeratin, EMA, TTF1, calretinin, smooth muscle actin, desmin and S100 protein; the epithelial cells were immunoreactive for cytokeratin, EMA and TTF1. We interpret this lesion as a peculiar pseudopapillary variant of solitary fibrous tumor, corresponding to what has been reported in the literature as pulmonary adenofibroma and fibroadenoma. The most important differential diagnostic considerations are briefly discussed.