Pleuropulmonary desmoid tumors: Immunohistochemical comparison with solitary fibrous tumors and assessment of β-catenin and cyclin D1 expression

Context. - Desmoid tumors arising in the lung and pleura are extremely rare and can resemble other, more common neoplasms native to these sites. Alterations of the adenomatous polyposis coli/β-catenin pathway have been detected in sporadic desmoid tumors and have been associated with nuclear accumulation of β-catenin and overexpression of cyclin D1. Objective. - To analyze the expression of β-catenin and cyclin D1 in desmoid tumors and solitary fibrous tumors (SFTs), and to compare the utilities of these substances for distinguishing between these entities with those of other, more commonly used stains. Design. - Formalin-fixed, paraffin-embedded sections of 4 desmoid tumors (1 pulmonary, 1 pleural, 2 pleural/chest wall), and 5 benign and 6 malignant SFTs of the pleura were immunostained for β-catenin, cyclin D1, ALK1, CD34, vimentin, desmin, smooth muscle actin, muscle-specific actin, S100, and pancytokeratin. Staining intensity and the percentage of stained tumor cells were assessed semiquantitatively. Results. - Diffuse moderate or strong nuclear staining for β-catenin was found in all desmoid tumors, 4 of 5 benign SFTs, and 2 of 6 malignant SFTs. All cases except 1 benign SFT showed concurrent cytoplasmic staining. Nuclear and cytoplasmic cyclin D1 staining was increased in all groups. The best distinction between desmoid tumors and SFTs was provided by CD34 (desmoid tumors, 0/4; SFTs, 8/11) and smooth muscle actin (desmoid tumors, 4/4; SFTs, 0/11). Conclusions. - Our findings suggest that alterations in the adenomatous polyposis coli/β-catenin pathway and cyclin D1 dysregulation may contribute to the pathogenesis of pleuropulmonary desmoid tumors and SFTs. CD34 and smooth muscle actin stains are particularly useful for differentiating between pleuropulmonary desmoid tumors and SFTs.