Myofibroblastoma of the breast mimicking carcinoma: a diagnostic challenge with a crucial role for histopathology and immunohistochemistry

Myofibroblastoma is a rare mesenchymal tumour known for its benign nature but complex diagnostic pathway. A woman in her 40s presented with a painless breast mass, initially reported as a fibroadenoma on ultrasound mammography and as a benign to borderline phyllodes tumour on fine needle aspiration cytology. Contrast-enhanced CT was reported as carcinoma of the breast with Breast Imaging and Reporting Data System (BIRADS)-6. Based on these findings, a modified right radical mastectomy was performed. This case highlights the limitations of radiological modalities in diagnosing myofibroblastoma due to its diverse morphological spectrum. The definitive diagnosis was established through extensive histopathological examination and immunohistochemistry, which demonstrated the tumour's unique immunoprofile, showing strong positivity for CD34 and focal positivity for desmin and Bcl-2. This case underscores the role of histopathology and immunohistochemistry in distinguishing myofibroblastoma from other breast lesions, emphasising the need for high diagnostic accuracy and thorough evaluation to guide appropriate management and avoid unnecessary, aggressive treatments.