Papillary pneumocytoma of the lung simulating a pleomorphic adenoma.

A rare case of papillary pneumocytoma of the lung is reported. The immunohistochemical positivities for EMA, cytokeratin and TTF-l strongly support the hypothesis that the neoplastic cells are originated from type 2 pneumocytes. The tumour also presented areas displaying stroma of non-specific mixoid appearance, simulating a benign tumour of the salivary gland type. We propose that these mixoid areas constitute structures of metaplastic origin.