Nodular fasciitis of the breast diagnosed by fine-needle aspiration cytology: A case report

Background : Nodular fasciitis is a benign disease characterized by reactive fibroblast proliferation and is also called pseudosarcomatous fibromatosis. Differentiation of nodular fasciitis from sarcoma is difficult. We report a rare case of estrogen receptor (ER)-positive nodular fasciitis of the breast diagnosed by fine-needle aspiration cytology (FNAC). Case : A 35-year-old woman presented with a 2×1×1.5 cm palpable, nonfixed nodule in the upper outer quadrant of the right breast. FNAC revealed the presence of many uniformly fusiform fibroblasts containing spherical and oval nuclei with inflammatory cells and myxoid substance in the background. On the basis of these findings, we made a diagnosis of nodular fasciitis (Class II). Core needle biopsy revealed numerous fibroblasts forming a “tissue culture-like” appearance, and inflammatory cells and interstitial myxoid substance ; findings that supported the diagnosis of nodular fasciitis. The nodule was suspected of being malignant clinically, and excisional biopsy was performed. The nodule proximal to the fascia was definitely diagnosed as ER-positive nodular fasciitis. Conclusion : We encountered a rare case of ER-positive nodular fasciitis that developed in the breast, and we diagnosed it as a nodular fasciitis based on the FNAC findings alone. The possibility of nodular fasciitis should always be kept in mind when performing FNAC of breast tumors.