LAUSR

Inflammatory myofibroblastic tumors of the uterus are uncommon mesenchymal neoplasms with intermediate malignant potential. Previously classified under 'inflammatory pseudotumors', inflammatory myofibroblastic tumors most commonly involve the lungs and intraabdominal soft tissue. Accurate identification is important given the risk of local recurrence (25%) and distant metastasis (2%). Approximately half of inflammatory myofibroblastic tumors harbor rearrangements in the anaplastic lymphoma kinase (ALK) gene on chromosome 2p23. ALK is a transmembrane tyrosine kinase which undergoes translocation with various fusion partners, resulting in the 3′ kinase portion of ALK being joined to the 5′ portion of a constitutively expressed gene, forming a fusion oncogene. A common breakpoint is intron19, resulting in dissociation of 3′ exons 20–29 from 5′ exons 1–19. Previously described fusion partners with ALK include IGFBP5, THBS1, FN1, and TIMP3. Unlike soft tissue or pulmonary inflammatory myofibroblastic tumors, ALK is the only receptor tyrosine kinase implicated in uterine inflammatory myofibroblastic tumors to date. In the extrauterine ALK negative inflammatory myofibroblastic tumors, rearrangements have been noted in ROS1, PDGFRB, RET, and NTRK11 genes. As in this case of a 37yearold who underwent laparoscopic myomectomy for a 6 cm fibroid, most uterine inflammatory myofibroblastic tumors are incidental pathological findings. Grossly, the tumor may be difficult to differentiate from a benign leiomyoma. Microscopically, the lesion demonstrated proliferation of myofibroblastic spindle cells, abundant eosinophilic cytoplasm, little nuclear atypia or mitotic activity, and no necrosis. Perivascular lymphoplasmacytic infiltrates (Figure 1) and focal Figure 1 Perivascular lymphoplasmacytic infiltrates (hematoxylin and eosin, ×40 magnification).