Anaplastic lymphoma kinase (ALK) expression in the inflammatory myofibroblastic tumor - A comparative immunohistochemical study

Inflammatory myofibroblastic tumor (IMT) is an uncommon mesenchymal neoplas m with a variable histologic appearance that may mimic other spindle cell p rocesses, particularly nodular fasciitis, desmoid tumor, and in intra-abdom inal locations, gastrointestinal stromal tumor. Recently, gene fusions invo lving ALK at chromosome 2p23 have been described in IMTs. The resultant ALK protein overexpression in the myofibroblastic component of these tumors is detectable by immunohistochemistry. We, examined 73 IMTs, 20 cases of nodu lar fasciitis, 15 desmoid fibromatoses, and 15 gastrointestinal stromal tum ors by immunohistochemistry using ALK-11, a rabbit polyclonal antibody that recognizes the C-terininus of the protein. ALK positivity was detected in 44 of 73 (60%) IMTs. All cases of nodular fasciitis, desmoid fibromatosis, and gastrointestinal stromal tumors were ALK negative (p < 0.001). These fi ndings demonstrate that ALK positivity is common in IMTs, and immunohistoch emistry using anti-ALK antibodies can be helpful, in the differential diagn osis of these neoplasms. In addition,, anti-ALK staining seems to correlate with those IMTs that have the typical tri-patterned histologic appearance and clinical presentation, providing additional support to the premise that IMT is a distinctive clinicopathologic entity within the broad category of inflammatory pseudotumors. Key Words: Inflammatory myofibroblastic tumor ( IMT)Inflammatory pseudotumor-Anaplastic lymphoma kinase (ALK)-Desmoid tumor -Gastrointestinal stromal tumor-Nodular fasciitis.