Superficial leiomyosarcoma: a clinicopathologic review and update.

Background: Superficial leiomyosarcomas (SLMSs) are rare soft tissue malignancies. A clinicopathologic review of 25 cases was undertaken.

Methods: Twenty-five cases diagnosed between 1990 and 2007 were reviewed. Clinical information was obtained from patient charts. Histologic slides were reviewed, and immunohistochemical stains were performed.

Results: All patients presented with a nodule. Fourteen tumors were confined to the dermis and 11 involved subcutaneous tissue. Smooth muscle markers were positive in all cases. CD117 was consistently negative. Novel histological features included epidermal hyperplasia, sclerotic collagen bands and increasing tumor grade with the depth of the lesion. Poor outcome was associated with size > 2 cm, high grade and depth of the lesion.

Conclusions: SLMSs are rare but important smooth muscle tumors of the skin. The clinical presentation may be non-specific. The histologic appearance is that of a smooth muscle lesion, but epidermal hyperplasia and thickened collagen bands are previously underrecognized features. Immunohistochemical stains are useful in confirming smooth muscle differentiation, but CD117 is of limited utility. SLMS can appear low grade or even benign on superficial biopsies, leading to undergrading or a delay in the correct diagnosis. Clinicians and pathologists alike should therefore be aware of these pitfalls and must approach these cases with caution.