Anatomic Pathology / REACTIVE SPINDLE CELL NODULES

Reactive spindle cell nodules (RSCNs) arising postoperatively or after fine-needle aspiration (FNA) have been reported previously in the genitourinary tract and thyroid. We describe 18 cases of similar lesions in breast, associated with a history of core needle biopsy or FNA. The majority of the RSCNs (15 cases) were associated with papillary lesions or complex sclerosing lesions. The RSCNs were nonencapsulated and relatively nodular, measuring 1.5 to 9 mm. They were composed of spindle cells with mild to moderate nuclear pleomorphism and a low mitotic count. A network of small blood vessels, macrophages, and lymphocytes was present in all cases. Immunohistochemically, the spindle cells expressed smooth and specific muscle actins, supporting a myofibroblastic origin. The association of RSCNs with needle trauma to fibrosclerotic lesions, such as complex sclerosing lesions and papillary lesions that regularly have myofibroblasts, suggests an exuberant reparative cause. Recognition of this reactive process will avoid overdiagnosis of mammary spindle cell malignant neoplasm. Postoperative spindle cell nodules were first described by Proppe et al1 in the genitourinary tract. More recently, Baloch et al2 described similar reactive spindle cell nodules after fine-needle aspiration (FNA) of the thyroid gland. Those lesions show exuberant proliferation of spindle cells with frequent mitoses and neovessels and can be misinterpreted as malignant neoplasms. FNA and core needle biopsies have been used extensively in the management of breast diseases.3-12 Complications related to these procedures have been studied thoroughly and are considered uncommon events of minor clinical implications. A variety of tissue changes have been described after FNA13,14 and core needle biopsy of the breast.15-17 The more common changes include hemorrhage, hemosiderin deposits, and infarction, and the less common include epidermoid inclusion cysts, pseudoaneurysm formation, and epithelial implantation.5,13,15-20 Fresh hemorrhage and destruction of lesions with hematoma formation also may be seen after FNA,13,14 and fibroblastic and vascular proliferation have been reported in the FNA or core needle biopsy site.14 However, proliferation of spindle cells to yield a tumor-like appearance, such as the reactive spindle cell nodules (RSCNs) developing after needle aspiration or surgery, has not been recognized in the breast to our knowledge. Most benign spindle cell lesions described in breast, including inflammatory pseudotumor,21-24 nodular fasciitis,25 fibromatosis,26,27 and myofibroblastoma28 develop spontaneously. We describe uncommon reactive spindle cell proliferations of the breast associated with previous needle biopsy trauma to lesions with fibrous stroma as an intrinsic element, such as papillomas and complex sclerosing lesions (CSLs). Our emphasis is on the histologic features and differential diagnosis of such cases. Anatomic Pathology / ORIGINAL ARTICLE Am J Clin Pathol 2000;113:288-294 289 © American Society of Clinical Pathologists Materials and Methods The files of the Breast Pathology Consultation Service at Vanderbilt University Medical Center, Nashville, TN, for the years 1994 through 1998 were reviewed. All cases with a diagnosis of reactive changes after FNA or stereotactic core needle biopsy, benign spindle cell lesions, and lowgrade spindle cell metaplastic carcinomas were retrieved. The slides were reviewed and, after assignment to recognizable or accepted neoplastic categories, 18 cases interpreted as reactive spindle cell proliferation were selected for study. The clinical history of trauma and FNA or core needle biopsy was obtained from referring pathologists or physicians responsible for patient care. Histologic evaluation was performed using H&E-stained sections, and the associated underlying breast lesions were noted using published diagnostic criteria.29-32 The following histologic features were analyzed: size of the spindle cell lesion, growth pattern, cellularity, nuclear atypia, and mitotic rate. The microscopic growth pattern was classified as nodular with relatively smooth borders or partially infiltrative. The overall cellularity was evaluated considering the area occupied by spindle cells compared with the area occupied by fibrous tissue. Nuclear pleomorphism was graded on a scale of 1 to 3, with 1 indicating nuclei that were uniform and small and 3 indicating larger nuclei and nuclei showing variation in shape and size. Areas of maximum mitotic activity were identified, and the number of mitoses was expressed per 10 high-power fields. The diameter of the high-power field was 0.49 mm (area, 0.20 mm2). The presence of the following other features was evaluated: glands entrapped in the needle tract, squamous metaplasia, inflammatory cells, foamy cells, hemosiderin-laden macrophages, edema, and acute hemorrhage associated with the spindle cell proliferation. Immunohistochemical stains ❚Table 1❚ were performed in 7 cases using a Ventana ES automated immunostainer (Ventana, Tucson, AZ) and the streptavidin-biotin-peroxidase method.