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Aims Nodular fasciitis is known to be a benign mimic of sarcoma, both clinically and histologically. Accurate diagnosis, particularly on small biopsies, remains a challenge, as the morphology can be varied and the immunophenotype is essentially non-specific. Recently, rearrangement of the ubiquitin-specific protease 6 (USP6) gene has been reported as a recurrent and specific finding in nodular fasciitis. The aim of this this study was to evaluate the diagnostic utility of USP6 fluorescence in-situ hybridization ( FISH) analysis in a subset of spindle-cell proliferations in which nodular fasciitis enters into the differential diagnosis. Methods and results A database search was performed at the Middlemore Hospital Histopathology Department. All in-house cases diagnosed between 2002 and March 2014 in which nodular fasciitis was considered as a differential diagnosis were retrospectively identified. Twenty cases were retrieved, reviewed and categorized as 'definite', 'possible' or 'definitely not' nodular fasciitis by consensus morphological opinion of three experienced pathologists. FISH analysis for USP6 rearrangement was performed in each case, with a commercially available break-apart probe. Of seven cases that were morphologically categorized as 'definite' nodular fasciitis, six were FISH-positive and one was FISH-negative. Of four cases categorized as 'possible' nodular fasciitis, one was FISH-positive and three were FISH-negative. Nine cases categorized as 'definitely not' nodular fasciitis were all FISH-negative. In the morphologically definitive cases, FISH analysis for USP6 had a sensitivity of 86% and specificity of 100% for a diagnosis of nodular fasciitis. The positive predictive value was 100%, and the negative predictive value 90%. Conclusions USP6 FISH is a useful ancillary test in cases where nodular fasciitis is a potential diagnostic consideration. [ABSTRACT FROM AUTHOR]

Aggressive angiomyxoma (AA) is a benign, slow-growing tumor that characteristically occurs in women of reproductive age. Local recurrence is cited in 30% to 40% of cases. Wide local excision is the treatment of choice. However, recent reports suggest a role for hormone manipulation in the management of these tumors. The morphology and immunophenotype of AA overlap with that of other, mainly benign vulvovaginal mesenchymal tumors. Diagnosis rests primarily on hematoxylin and eosin staining features, and distinction is important in determining appropriate treatment and follow-up. Rearrangement of HMGA2 has been shown in AA, and reports suggest that HMGA2 immunohistochemistry may have a role in the routine diagnosis of AA, its distinction from mimics, and in the evaluation of margins. Furthermore, CDK4 immunopositivity has been described in AA. We describe a series of 9 cases of AA with typical histology and long-term follow-up, and evaluate the role of HMGA2, CDK4, estrogen, and progesterone immunohistochemistry. One of 9 women (11%) experienced recurrence, with the second at 17 years, which is the longest recorded in the English literature. HMGA2 immunohistochemistry was positive in 37.5% of cases, consistent with the reported frequency of HMGA2 gene rearrangement, and negative in all benign mimics. CDK4 immunoreactivity was weak, diagnostically not helpful, and of uncertain significance. Immunohistochemistry for estrogen and progesterone were positive in 87.5% of AAs, and were widely positive in control groups.