Mammary myofibroblastoma: Presentation of case.

INTRODUCTION AND IMPORTANCE: Mammary myofibroblastoma (MFB) is a rare benign mesenchymal lesion. It belongs to the family of benign spindle cell tumours of the mammary stroma and may exhibit confusing variants. Some of them may mimic invasive tumours, leading to the diagnostic dilemmas, especially in core needle biopsy specimens or frozen sections. Familiarity with the characteristics of this tumour is of great importance for accurate diagnosis and proper treatment. CASE PRESENTATION: We report about a rare form of CD34-negative mixed epithelioid/lipomatous form of mammary myofibroblastoma in a 48-year-old Caucasian premenopausal woman with no previous medical history. Breast imaging suggested a benign lesion. The core needle biopsy suggested breast MFB. The definitive diagnosis was established through histopathology and immunohistochemistry of the lumpectomy specimen. CLINICAL DISCUSSION: Despite its rarity, breast MFB is a disease with a wide spectrum of histologic morphologies. CD34 positivity is seen in majority of MFB cases. MFBs uncommonly show absent expression of CD34, a potential diagnostic pitfall, just like in our case. CONCLUSION: Pathologists should recognise the wide range of differential diagnoses and be familiar with the diverse morphological appearances of these lesions to make an accurate diagnosis. Surgical excision is at present the ordinary treatment of MFB.