Inflammatory pseudotumour and myofibroblastic tumour of the respiratory tract: just one entity?

Background. The nature and the cell of origin of lesions variously described as inflammatory pseudotumour (IP), pseudosarcomatous proliferation or inflammatory myofibroblastic tumour (IMT) are still debated. Most cases behave as benign, reactive lesions, but rarely may have an aggressive course. We analysed the clinicopathological and molecular features of a series of IMTs of the respiratory tract, with the aim to verify if they represent a single entity or a heterogeneous group of lesions. Methods. Histological features of thirty-eight cases diagnosed as IMT or IP in various Institutions were reviewed. Immunohistochemistry was performed for the following antibodies: CAM 5.2, MNF116, CD34, CD21, CD35, betacatenin, CD68, HHV8 and 6, smooth muscle actin, desmin, ALK, ki67, IgG4. Molecular investigations included in situ hybridization for EBV and DNA sequencing for c-kit, cmet, EGFR, PDGFR alpha and beta. Results. Histologically, tumours were subdivided in two groups: type A (8 cases) included lesions with a predominance of inflammatory cells and no prominent spindle cell proliferation; type B (27 cases) included lesions composed of uniform proliferation of spindled cells, sometimes with myxoid features. Three cases had borderline features between type A and B and were classified as “type AB”. All cases were negative for cytokeratins, HHV8, HHV6 and CD21 and beta-catenin. Cases from all subtypes were variously positive with muscular markers, CD34, CD68 and IgG4. ALK antibody stained only 4 cases of B type. No cases showed mutations in the genes studied.Conclusions. Under the designation of IMT or IP are actually included different lesions. In the present series, we identify histologically two main groups: one which represents more likely true myofibroblastic tumoral proliferations, and a group which is represented by non-tumoural, reactive lesions. At moment, however, it appears that there are no immunohistochemical or molecular markers to distinguish the two types of lesions.