Superficial leiomyosarcoma (SLMS) is a rare sarcoma, which is further classified as either cutaneous or subcutaneous based on dermal location and site of origin. Cutaneous SLMS have excellent outcome with rare recurrence, whereas subcutaneous SLMS have high recurrence and metastatic rates. Wide excision with 2-5cm margins has historically been advocated for treatment for both subtypes. However, due to the low recurrence and metastatic potential of cutaneous SLMS more conservative excisional margins may be more appropriate and is supported by recent institutional-based studies.

Case Report

A 74-year-old white man presented with an asymptomatic, new lesion of six months duration on his right upper back. Physical examination revealed a 5mm tan colored papule. His past dermatologic history is significant for actinic keratoses and his medical history is non-contributory. He denied a history of non-melanoma skin cancer or other cutaneous neoplasms. A shave biopsy was performed with dermatopathologic examination and immunohistochemistry staining. Histological examination revealed fascicles of atypical spindle cells present within the dermis (Figures 1,2). Many cells demonstrated hyperchromatic and pleomorphic nuclei (Figure 3). Immunohistochemical stain for desmin was strongly positive and was weakly positive for smooth muscle actin. A diagnosis of cutaneous SLMS was rendered. After review of current guidelines, treatment included a wide local excision with 1cm margins. Temporary wound closure was maintained with subcutaneous sutures. Histologic examination of the surgical specimen revealed the margins free of tumor and the defect was then closed primarily with subcutaneous sutures and a running, interrupted subcuticular suture with excellent wound approximation and tissue eversion. No recurrences were noted at 12-month follow-up examination.

Discussion

Leiomyosarcomas are sarcomas of smooth muscle, which are classified as superficial or metastatic depending on the site of origin (Table 1). ¹Superficial leiomyosarcoma is an extremely rare sarcoma and the incidence is not known or reported in the literature due to its rarity. It often arises on hair-bearing skin of middle-aged men. ² SLMS is often asymptomatic but may present with mild tenderness, pruritus bleeding, and slow growth. Clinically, the differential diagnosis includes many benign cutaneous tumors including irritated seborrheic keratosis, cysts, lipomas, neurofibromas, dermatofibromas, and carcinoma. Histologic examination is strikingly significant for a proliferation of pleomorphic fascicles of spindle cells in the dermis. Immunohistochemistry is necessary for diagnosis as many spindle cell neoplasms mimic SLMS, such as spindle cell squamous cell carcinoma, atypical fibroxanthoma, and desmoplastic melanoma. ^3-4 SLMS is further subdivided into cutaneous and subcutaneous SLMS and this distinction is based on their location in the dermis and presumed site of origin (Table 2). ⁴ This classification is of prognostic significance as the biologic behavior of these two subtypes diverges greatly. ^3-6Cutaneous SLMS is postulated to arise from the arrector pili muscles and is located in the dermis whereas subcutaneous SLMS arises from the endothelium of dermal vessels and has extension into the subcutaneous tissues. ⁷ Furthermore, cutaneous SLMS has an excellent prognosis with variable recurrence rates and only isolated reports of metastases, whereas subcutaneous SLMS has a grimmer prognosis with reported recurrence of 50 percent and 30-40 percent reported incidence of metastases. ^6,8-10

Surgical excision is the standard of care for SLMS, however, recommended excisional margins and follow-up are poorly defined. Historically, recommended margins ranged from 2-5cm for both cutaneous and subcutaneous SLMS with no criteria outlined for narrower verses wider margins. As the prognosis differs significantly between these two subtypes, excisional margins should be recommended for each separately. A recent analysis of 33 patients' cutaneous SLMS reported excellent outcomes with wide local excision with 1cm margins and no reported recurrences nor metastases at a median follow-up time of 15.5 months. ⁶ This observation is supported by other large institutional based studies in the literature. ^5,9 We recommend pathologic evaluation using the en face technique of the peripheral and deep margin with immunohistochemical staining, as this would allow more complete margin assessment. ¹¹ Although this was not performed in this case, it was requested. This should result in high cure rates and better margin control.

In conclusion, superficial leiomyosarcoma is a rare soft tissue sarcoma with poorly defined treatment algorithms. Cutaneous SLMS has an excellent prognosis and low recurrence rates with narrow excisional margins. Dermatopathology controlled surgical excision proves to be a viable approach to decrease recurrence and increase patient outcomes.

Brooke Walls is PGY3 at Nova Southeastern University College of Osteopathic Medicine and David Dorton, DO is Attending Physician at Bay Dermatology.

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