Post-traumatic inflammatory pseudotumor of the breast with atypical morphological features: A potential diagnostic pitfall. Report of a case and a critical review of the literature.

Although inflammatory pseudotumor (IPT) and inflammatory myofibroblastic tumor (IMT) may share a common morphology, they are distinct clinico-pathologic entities. Unfortunately, the terms IMT and IPT are still used interchangeably, especially when lesions occur in unusual sites, including breast. All the cases of IMT/IPT involving the breast have raised spontaneously without any apparent prior injury. We herein report the first case of a post-traumatic IPT of the breast parenchyma in a 22-year-old male. Histologically, the lesion was highly cellular and composed of spindle cells arranged in a predominant fascicular pattern. Notably, mono- or multi-nucleated large pleomorphic cells were observed. Inflammatory cells, especially plasma cells and lymphocytes, were closely admixed with the spindle cell proliferation. The overall picture was reminiscent of an "IMT with atypical features", typically seen in lung, abdomen, pelvis, and retroperitoneum of children. Immunohistochemically, the spindle-shaped and large pleomorphic cells were immunoreactive to vimentin, α-smooth muscle actin, and desmin. No immunoreactivity was obtained with ALK-1 protein. The present case contributes to widening the morphological spectrum of IPT of the breast, emphasizing the possibility that a reactive lesion may contain large pleomorphic cells that may represent a potential diagnostic pitfall. Lastly, we suggest that the diagnosis of IMT of the breast should be rendered with caution when dealing with ALK-negative spindle cell lesions in adult patients, and alternative diagnoses, including IPT, should be seriously considered.