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Background: Differential diagnosis and detection of malignant lesions in mammography poses a challenge for many diagnosticians. Although mammography continues to be the best and cost-effective way to detect breast cancer, it has its limitations due in part to the radiological appearance of changes of a very rare condition. We are presented with changes that have met well-known radiologic criteria for the diagnosis of malignancy, yet they turn out to be benign, because they belong to a group of extraordinary lesions. Case Report: In June 2010, a 56-year-old woman found a lump in her right breast. Mammography performed at another medical center, revealed a change 12 mm in diameter, rated as BI-RADS 4C. Physical examination revealed a palpable lesion, 15 mm in diameter. Ultrasonography revealed hypoechogenic change with ill-defined outlines, size 14×10 mm - BI-RADS 5. Fine needle aspiration biopsy was done and revealed no atypical cells. The patient underwent an open surgical biopsy and a histopathological diagnosis was suggested to be a type of Wegener's granulomatosis. Exclusion of cancer enabled the continuation of medical treatment of the underlying disease. There were no changes in the breast in follow-up studies. Conclusions: The differential diagnosis of breast tumors should include rare conditions that can sometimes mimic breast cancer. One of them is Wegener's granulomatosis. Both, the diagnosis and treatment of the disease, require the cooperation of specialists from various fields, including clinicians, pathologists and radiologists.