Calcifying fibrous pseudotumor versus inflammatory myofibroblastic tumor: A histological and immunohistochemical comparison

Calcifying fibrous pseudotumor (CFP), a recently described lesion, is chara cterized by a predominantly lymphoplasmacytic infiltrate with abundant hyal inized collagen and psammomatous or dystrophic calcifications. The cause an d pathogenesis are unclear, but it has been postulated that CFP may represe nt a sclerosing end stage of inflammatory myofibroblastic tumor (IMT). We c ompared the histological and immunohistochemical profiles of seven cases di agnosed as CFP and seven as IMT. Histologically, the CFP demonstrated varyi ng degrees of calcifications in addition to fibroblastic proliferation admi xed with inflammatory cells composed of lymphocytes, eosinophils, and mast cells. The IMTs rarely contain calcifications and had a myofibroblastic pro liferation varying from hyalinized acellular collagen to florid fibroblasti c proliferations simulating sarcoma. The inflammatory component was compose d primarily of plasma cells and lymphocytes, sometimes arranged as lymphoid aggregates with germinal centers. All CFP cases were diffusely positive fo r factor XIIIa and negative for smooth muscle actin, muscle-specific actin, and CD34. All IMTs demonstrated diffuse positivity for actin, variable pos itivity for CD34, and focal positivity for Factor XIIIa. This study demonst rates certain distinct histologic, immunohistochemical, and electron micros copic features between IMTs and CFPs.