Primary Undifferentiated Malignant Tumor of the Anterior Mediastinum in a Patient with Remote History of Breast Carcinoma: A Diagnostic Challenge

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Anterior mediastinal masses present a wide differential diagnosis and can pose significant diagnostic challenges.We report a case of a 53-year-old female with a remote history of treated invasive ductal carcinoma of the breast, who presented with dry cough.Imaging revealed a 5.1 cm anterior mediastinal mass adjacent to the aortic arch.Endobronchial ultrasound-guided transbronchial needle aspiration was non-diagnostic.CT-guided biopsy demonstrated an undifferentiated malignant tumor.Immunohistochemistry showed positivity only for vimentin, while epithelial, lymphoid, neuroendocrine, mesothelial, and breast markers were negative, excluding common mediastinal tumors and metastasis.The lesion was diagnosed as a primary undifferentiated mediastinal sarcoma, likely undifferentiated pleomorphic sarcoma.The patient was started on paclitaxel and carboplatin.This case highlights the importance of comprehensive immunohistochemical evaluation in mediastinal masses, especially in patients with prior malignancy.