Document Type

Article

Publication Date

7-2-2008

Abstract

Inflammatory myofibroblastic tumor (IMT) is a rare soft tissue tumor composed of myofibroblasts with an inflammatory infiltrate. Various gene fusions involving the anaplastic lymphoma kinase (ALK) gene at chromosome 2p23 have been described in IMT, suggesting a neoplastic etiology. The ALK rearrangement is reportedly more common in children and there are only rare IMTs in adults with genetic information. This study represents the largest series of lesions designated as IMT on morphologic grounds with comparative ALK IHC and FISH analysis. Sixteen IMTs were retrieved from the UNM and UVa archives. Inclusion criteria required spindle cells, inflammatory cells and thorough clinical, histological and immununohistochemical exclusion of other diagnostic possibilities. IHC was performed on each of the sixteen cases using a monoclonal ALK1 antibody and evaluated for cytoplasmic and nuclear stain intensity and distribution. FISH was performed on tissue microarray sections using the ALK breakapart genomic marker. MetaSystems automated FISH analyzer detected signal patterns on interphase nuclei and results were interpreted on a Meta workstation. Patients ranged in age from 2-70 years (mean 48; median 43). IHC and FISH were successful on 16/16 and 10/16 cases, respectively. One case was positive for ALK rearrangement by FISH. This case also demonstrated diffusely strong cytoplasmic and focally strong nuclear immunopositivity. One case showed diffusely strong cytoplasmic ALK immunopositivity without gene rearrangement by FISH. ALK overexpression (IHC) and genomic rearrangements (FISH) are uncommon in our series of IMTs. This may be related to the older age of patients in our study. ALK IHC negative cases did not show ALK gene rearrangement by FISH. Further investigation is warranted to determine if ALK positive lesions represent a different, more biologically aggressive entity, necessitating a distinct designation.

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