A spontaneously resolving breast lesion: imaging and cytological findings of nodular fasciitis of the breast with FISH showing USP6 gene rearrangement.

We report a case of nodular fasciitis of the breast in a 48-year-old woman who presented with a tender rapidly growing right breast lump. Ultrasound guided fine needle aspiration (FNA) of the solid mass was performed. Cytology was reported as atypical spindle cell neoplasm and the patient was referred to a breast surgeon at a tertiary institution for a definitive diagnosis and further management. Follow-up ultrasound showed partial regression and MRI, mammogram after 2-3 weeks confirmed spontaneous and total resolution of the lesion. Nodular fasciitis of the breast is rarely diagnosed on cytology alone and a histological diagnosis is usually required for a definitive diagnosis. However, in this case, the lesion spontaneously resolved prior to core biopsy or diagnostic open biopsy. The cytological features in conjunction with immunohistochemistry and the clinical history strongly suggest nodular fasciitis, which is further supported by a USP6 FISH positive result.