Nodular fasciitis of the breast clinically resembling breast cancer in an elderly woman: a case report

Nodular fasciitis is a benign reactive proliferative lesion of fibroblast cells, which can occur throughout the body. However, it has rarely been reported in the breast of an elderly woman. Our patient was an 88-year-old Asian woman who had noticed a mass in her right breast for 1 month before presentation to our hospital. The mass was elastic-hard and 20 mm in size. No qualitative diagnosis was made by core needle biopsy. Because of potentially malignant findings on mammography and ultrasonography, she underwent an excisional biopsy. Microscopically, spindle cell proliferation with abundant elastic fibers were observed. The tumor cells were positive for α-smooth muscle actin and negative for pancytokeratin, β-catenin, and cluster of differentiation 34. Based on these morphological and immunohistochemical features, a diagnosis of nodular fasciitis was made. All resection margins in the specimen were tumor-free. The patient has been disease-free for over 12 months. Nodular fasciitis shows clinical features and imaging findings similar to those of breast cancer. To avoid unnecessary surgery, nodular fasciitis should be taken into consideration when there is spindle cell proliferation found by biopsy.