Inflammatory Myofibroblastic Tumor of the Breast Coexisting with Pseudoangiomatous Stromal Hyperplasia

Inflammatory myofibroblastic tumors (IMTs) are uncommon breast lesions that consist of spindle cells accompanied by plasma cell-rich inflammatory infiltration, which may mimic breast cancer clinico-radiologically. A woman aged 38 years with a breast mass was referred to our general surgery clinic. The physical examination revealed a mass with irregular borders in the upper outer quadrant of the left breast. In mammography, the lesion was 15 mm in diameter with a spheric form and high density. Ultrasonographically, the mass was solid, heterogeneous, and hypoechoic with posterior enhancement. Histopathologic examination of a core needle biopsy revealed a proliferation of spindle cells with eosinophilic cytoplasm and mild nuclear atypia, which showed negative immunostaining for pancytokeratin, HMWCK, CAM5.2, p63, CD34, β-catenin, and ALK but diffuse positivity for smooth muscle alpha (SMA). The lesion was reported as a "spindle cell lesion" and excision with clear margins was recommended. In the lumpectomy specimen, the lesion consisted of spindle cells that formed fascicles and infiltrated the surrounding breast parenchyma. Lymphocytes and plasmocytes scattered among spindle cells were noted. Necrosis, increased mitotic activity, nuclear pleomorphism and hyperchromasia were not detected. Immunohistochemical findings were the same in the core needle biopsy. The Ki-67 proliferation index was below 5%. With these findings, differential diagnoses were ruled out and the tumor was reported as IMT. In close proximity to this lesion, areas of columnar cell lesion with atypia and surrounding pseudoangiomatous stromal hyperplasia were seen. Patient has a follow-up of 16 months without recurrence.