[58] Myofibromas with Atypical Features: Expanding the Morphologic Spectrum of a Benign Entity

Konstantinos Linos, Jodi M Carter, Andrew L Folpe, Sharon W Weiss, Mark A Edgar. Emory University, Atlanta, GA; Mayo Clinic, Rochester, MN

Background: Typical myofibromas are biphasic tumors having a peripheral myoid cuff and a central zone of immature spindled/rounded cells. A subset of myofibromas display various atypical features that lead to a misdiagnosis of sarcoma. To more completely characterize these tumors and define their behavior we analyzed our experience with myofibromas having one or more atypical features.
Design: Out of 267 cases of myofibromas in our consultation files, 25 cases were retrieved based on reports in which atypical features were mentioned. Hematoxylin and eosin stained slides and immunostains were reviewed. Available follow-up information was obtained.
Results: The tumors presented in 15 males and 8 females [gender unknown in 2] (mean age 21 yrs; range 5 months-72 yrs) as masses of variable size (mean 2.8 cm; range 1.2 to 6.5 cm). Fourteen cases arose on the head and neck (mandible 5, tongue 2, neck 2, zygomatic bone 1, parotid 1, eyelid 1, cervical vertebra 1, scalp 1) and 11 cases on the limbs (arm 2, forearm 2, hand 3, wrist 1, foot 2, calf 1). Grossly, the lesions were tan-white to red/brown and firm. The referring or suspected diagnosis was sarcoma in 9 cases. The tumors were composed of sheets and fascicles of spindled to ovoid cells situated around a pericytomatous vasculature (19/25) with peripheral or interspersed myoid nodules (21/25) and necrosis (5/25). No tumor had significant nuclear atypia. Atypical features included hypercellular areas with a primitive appearance (20/25), infiltrating borders (19/25), intravascular growth (6/25) and perineural invasion/nerve entrapment (6/25). The mean mitotic rate was 5 mitoses/10HPF. The tumors were positive for SMA (10/10) and CD34 (2/8) and negative for other markers. Follow up in 5 patients (median 33 mos; range 2-92 mos) revealed no local recurrences or distant metastases.
Conclusions: A small subset of myofibromas display atypical features which include primitive-hypercellular areas, mitotic activity, infiltrating borders, intravascular growth and perineural invasion/entrapment and which may lead to a diagnosis of sarcoma. Based on preliminary follow up information these tumors pursue a benign course and should be included in the morphologic spectrum of classic myofibroma.
Category: Bone & Soft Tissue

Monday, March 4, 2013 1:00 PM

Poster Session II # 23, Monday Afternoon


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