Fig. 2.

At histology the pulmonary lesion are characterized by a dense and diffuse infiltrate of monomorphic lymphocytes and plasma-cells. The lymphoid population is composed of small lymphocytes with a moderate rim of clear cytoplasm obliterating the alveolar spaces (A). The mucosa of bronchial wall reveal lympho-epithelial lesions strongly indicative of extra-nodal MALT lymphoma (B). At immunohistochemistry, neoplastic cells are diffusely positive for CD20, demonstrating the B-cell phenotype and the clonal nature (CD20 immunohistochemistry, Hematoxylin counterstain, 20X (C). Mitotic activity evaluated with MIB-1/Ki-67 is low (3-5%) (MIB1 immunohistochemistry, Hematoxylin counterstain, 20X (D)