Nodular fasciitis of the breast: a clinicopathological and genetic analysis of seven cases

Abstract

Objective: To investigate the clinicopathological and genetic features of nodular fasciitis of the breast (NFB). Methods: The clinical and histologic features of seven NFBs were retrospectively reviewed. Immunohistochemistry, fluorescence in situ hybridization (FISH) and reverse transcription-polymerase chain reaction (RT-PCR) were performed. Results: All the seven patients were female, with a mean age of 36 years (range from 15 to 51 years). The duration of the lesion ranged from 10 days to 2 years. There was no history of trauma for all patients. The lesions occurred in the upper quadrant (4 cases), the lower quadrant (2 cases) and the axillary tail region (1 case). The maximum diameter was 1.0-3.5 cm. All cases showed similar morphology as nodular fasciitis occurring elsewhere in the body. They were composed of plump spindle cells arranged in short bundles or fascicles within a loose collagenous/myxoid stroma. Erythrocyte extravasation, mixed chronic inflammatory cells infiltration and microcystic changes were typically seen. Mitoses were present, with no atypical mitoses observed. The spindle cells were positive for smooth muscleactin(SMA, 6/6), CD10(2/3), and negative for desmin, β-catenin, CD34, CKpan, EMA, S-100, p63 and ALK-1.The Ki-67 index were 5%-15%. USP6 gene rearrangement was found in six cases and MYH9-USP6 gene fusion in two cases. Local resection was performed in six cases. Spontaneous regression was observed in one case. Follow-up of all seven cases revealed no recurrence or metastasis. Conclusions: Although rare, NFB can mimic breast cancer clinically, radiologically and histologically. It should be always considered in the differential diagnosis for the spindle cell proliferations of the breast. A diagnosis of NFB can be achieved basing on the typical clinicopathological presentation. FISH detection of USP6 gene rearrangement in challenging cases is of great value.