[Adult myofibroma: a clinicopathological analysis of 15 cases]

Objective: To investigate the clinicopathological features and immunophenotype of adult myofibroma with emphasis on its differential diagnosis. Methods: The clinical, pathologic data and immunohistochemical profiles were analyzed in 15 cases of adult myofibroma diagnosed between 2014 and 2020 in Department of Pathology, Fudan University Shanghai Cancer Center. The literature was reviewed. Results: There were seven males and eight females, with age at presentation ranging from 22 to 74 years (mean 54 years; median 57 years). Tumor occurred principally in the extremities (n=9), less frequently involved the head and neck region (n=3) and trunk (n=2); one case was located in the vertebral canal of C6-7. Fourteen cases were solitary; one case was multifocal. Most patients presented with a slowly growing painless subcutaneous nodule, about 1 to 2 cm in size. One patient with multifocal disease and the patient with spinal lesion complained of intermittent pain. The duration of symptoms ranged from 2 months to 10 years. Microscopically, they were well circumscribed. All cases showed biphasic growth pattern, consisting of relatively well-differentiated eosinophilic nodules alternating with dark-staining primitive-appearing areas. The light-staining hypocellular nodules were composed of myofibroblast-like plump spindle cells within an eosinophilic stroma, which assumed pale blue myxochondroid appearance and hyalinization of varying degree. The dark-staining areas were composed of compact short spindled to ovoid cells with hyperchromatic nuclei and low mitotic activity, frequently showing a distinctive hemangiopericytoma-like architecture. By immunohistochemistry, the myoid spindled cells and the primitive cells stained variably for α-SMA, MSA and calponin, but were consistently negative for desmin and β-catenin. Conclusions: Adult myofibroma tends to occur in the middle to old aged patients with a predilection for the dermis or subcutis of the extremities. It is a benign neoplasm which can be cured by excision in most cases. Familiarity with its distinctive clinicopathological features helps in the distinction from other myofibroblastic neoplasms.