Inflammatory Myofibroblastic Tumor of the Placenta: A Report of a Novel Lesion in 2 Patients.

Inflammatory myofibroblastic tumor has been described in a wide variety of anatomic sites, although in the gynecologic tract, it has mostly been documented in the uterus, and has never been described in the placenta. Two patients presented with well-circumscribed placental masses that showed classic histologic features of inflammatory myofibroblastic tumor including a proliferation of myofibroblastic cells, a mixed inflammatory infiltrate, and a myxoid background. One case was positive by immunohistochemistry for anaplastic lymphoma kinase (ALK-1), whereas the other was negative by immunohistochemistry and fluorescent in situ hybridization. Inflammatory myofibroblastic tumors should be differentiated from other more aggressive uterine tumors that may involve the placenta by direct extension/metastasis because they can be managed conservatively, and in these 2 cases, did not seem to affect the course of the patient's pregnancies.