Cellular myxoma of soft tissue: a clinicopathological study of 38 cases confirming indolent clinical behaviour

Cellular myxoma of soft tissue: a clinicopathological study of 38 cases confirming indolent clinical behaviour Aims: To characterize the clinicopathological features and biological potential of a group of soft tissue lesions with morphology intermediate between intramuscular myxoma and low‐grade myxofibrosarcoma. Methods and results: Thirty‐eight lesions in 37 patients were retrieved from the authors’ consultation files. Clinical and follow‐up data were obtained and the lesions were also studied immunohistochemically. Tumours occurred in adults aged 25–83 years (mean 51.9 years) with a slight predominance in females. All cases, except two, were solitary. The extremities were preferentially involved (18 lower limb; nine upper limb), with seven lesions arising around the upper (2/7) and lower limb (5/7) girdles and four lesions occurring at other locations. Twenty‐nine of 31 of the tumours, for which the depth was known, were situated deep to the superficial fascia, although only 19 were strictly intramuscular. Histologically these lesions were both more cellular and more vascular than intramuscular myxoma, while lacking the cytological pleomorphism, nuclear atypia and curvilinear vascular pattern characteristic of low‐grade myxofibrosarcoma. CD34 positivity in lesional cells was identified in 17/30 (57%) cases, probably reflecting their fibroblastic nature. Staining for α‐smooth muscle actin was focally positive in 3/30 (10%) cases, while desmin and S100 protein staining were consistently negative. Clinical follow‐up data (available in 22 cases; median duration 30 months) demonstrate that these lesions behave in a benign fashion with only a small risk of local recurrence if not excised completely; in this study only two tumours recurred, both of which originally had been incompletely excised. None metastasized. Conclusions: The risk of recurrence in this group of lesions which we have designated ‘cellular myxoma’ appears to be low. Consequently simple complete local excision is most often adequate treatment. Longer follow‐up (5–10 years or more) in a larger number of cases will be important in more definitively confirming the natural history of these lesions.