Myofibroblastoma and solitary fibrous tumour of the breast: histopathologic and immunohistochemical studies

Thirteen mesenchymal tumours of the breast were reviewed histologically and immunohistochemically. Nine tumours (male:female ratio 5:4, average age 64 years) were classified as myofibroblastomas and presented as a single nodu le (four) or a multilobular mass (five). They were composed of elongated ce lls with vesicular nuclei showing grooves, intranuclear inclusion, and smal l but conspicuous nucleoli resembling myofibroblasts seen in scar tissue. I n six tumours, hyper-cellular zones alternated with paucicellular, hyaliniz ed areas. The collagen pattern was dense, diffuse, and brightly eosinophili c in all neoplasms. The tumour cells were positive for desmin, actin, and v imentin in all nine lesions, and in six tumours a focal CD 34 positivity wa s also demonstrated. Four tumours (four female patients, average age 75 yea rs) were classified as solitary fibrous tumours and consisted of well-circu mscribed nodules. They were characterized by a monomorphic population of th in, spindled to ovoid cells with finely dispersed chromatin and inconspicuo us nucleoli. The pattern of the collagen in these tumours was one of thick, brightly eosinophilic bands. These four tumours were negative for all mark ers tested except vimentin and CD 34. Although myofibroblastomas and solita ry fibrous tumours of the breast share many morphologic features, there are enough differences in their cytologic composition and, most importantly, i n their immunohistochemical profile to consider them as distinct entities. (C) 2000 Harcourt Publishers Ltd.