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pulmonary inflammatory myofibroblastic tumor

Friday 7 December 2007

Pulmonary IMT, pulmonary plasmocytic granuloma, pulmonary inflammatory pseudotumor

Digital case

- JRC:6390 : Pulmonary inflammatory pseudotumor - Myofibroblastic type.

Definition: Inflammatory myofibroblastic tumors are uncommon lesions composed of spindled myofibroblasts within a variable background of collagen and inflammatory cells.

Inflammatory myofibroblastic tumor of the lung occurs in all age groups without gender bias but, most commonly, in individuals under 40 years of age.

Microscopically, inflammatory myofibroblastic tumor is composed of a proliferation of spindled myofibroblasts within a variable background of collagen and inflammatory cells.

Although the pathogenesis of these lesions is not fully elucidated, recent studies suggest they may be neoplastic proliferations with potential to invade the mediastinum, hilar lymph nodes, and diaphragm.

Molecular types

- ALK+ pulmonary inflammatory myofibroblastic tumor
- ALK- pulmonary inflammatory myofibroblastic tumor

ALK rearrangements

Although the true nature of these lesions is not fully elucidated, identification of consistent cytogenetic alterations in the anaplastic lymphoma kinase (ALK) gene suggests that they may be neoplastic.

The neoplasia concept is supported by the presence of cytogenetic alterations in the anaplastic lymphoma kinase (ALK) gene, including TPM3–ALK, TPM4–ALK, and CLTC–ALK fusions, and ALK protein expression.

Clonal aberrations in the 2p23 and ALK gene regions have been demonstrated in both pulmonary and extrapulmonary inflammatory myofibroblastic tumors.

Viral infections, in particular human herpesvirus-8 (HHV-8), have been implicated in inflammatory myofibroblastic tumor pathogenesis.

HHV-8 infection

A small number of inflammatory myofibroblastic tumors have been reported to harbor human herpesvirus-8 (HHV-8), implicating the virus in its pathogenesis.

HHV-8 infects a wide range of normal cells including endothelial cells, lymphoid cells, dendritic cells, and fibroblasts. This parallels the spectrum of the neoplasms with a well-established role for HHV-8 in their pathogenesis, including Kaposi sarcoma, primary effusion lymphoma, and multicentric Castleman disease. HHV-8 infection of human fibroblasts is well documented in experimental studies.

It is known that the virus enters cells utilizing receptor-mediated endocytosis and displays activation of lytic and persistence of latent genes.

In light of these findings, inflammatory myofibroblast tumor appears to be a reasonable choice for HHV-8 testing.

Gómez-Román et al, reported HHV-8 deoxyribonucleic acid (DNA) sequences in seven cases of inflammatory myofibroblast tumor, and also identified viral transcripts from several open reading frames (ORF).

In the English language literature, only three additional cases of pulmonary inflammatory myofibroblastic tumor have been studied for HHV-8 by immunohistochemical and molecular methods.

One study has documented the absence of HHV-8 in pulmonary inflammatory myofibroblastic tumors, suggesting that further investigation is required to clarify the pathogenesis of this lesion. (17643094)

See also

- inflammatory myofibroblastic tumor

References

- Inflammatory myofibroblastic tumor versus IgG4-related sclerosing disease and inflammatory pseudotumor: a comparative clinicopathologic study. Yamamoto H, Yamaguchi H, Aishima S, Oda Y, Kohashi K, Oshiro Y, Tsuneyoshi M. Am J Surg Pathol. 2009 Sep;33(9):1330-40. PMID: 19718789

- Absence of human herpesvirus-8 in pulmonary inflammatory myofibroblastic tumor: immunohistochemical and molecular analysis of 20 cases. Tavora F, Shilo K, Ozbudak IH, Przybocki JM, Wang G, Travis WD, Franks TJ. Mod Pathol. 2007 Sep;20(9):995-9. PMID: 17643094 (Free)

- A case of an inflammatory myofibroblastic tumor in the lung which expressed TPM3-ALK gene fusion. Kinoshita Y, Tajiri T, Ieiri S, Nagata K, Taguchi T, Suita S, Yamazaki K, Yoshino I, Maehara Y, Kohashi K, Yamamoto H, Oda Y, Tsuneyoshi M. Pediatr Surg Int. 2007 Jun;23(6):595-9. PMID: 17063337

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