A man with skin tumours on the right thigh

Question

What is your diagnosis?

Diagnosis

Superficial cutaneous leiomyosarcoma (SCLM).

Discussion

Based on the history of recurrence, clinical manifestations and pathology, the patient was diagnosed with SCLM rather than skin leiomyoma. Both skin leiomyosarcoma and skin leiomyoma are types of smooth muscle tumours, and they express smooth muscle-specific markers such as smooth muscles actin (SMA), desmin and calponin. However, in comparison to leiomyoma, leiomyosarcoma typically displays a larger size, significant cellular atypia, a higher mitotic rate, infiltrative growth pattern, necrosis and vascular invasion.^1,2

Cutaneous leiomyosarcoma is a rare malignant tumour that may be easily misdiagnosed due to its rarity and non-specific clinical manifestations.² It is important to recognise the misleading features of this tumour. SCLM can occur in any area with hair, but it is more prone to occur in areas with a high density of hair follicles and arrector pili muscles, especially on the extensor surfaces of the lower extremities.³ The tumour in this patient occurred on the thigh, which is a predilection site. The common clinical differential diagnoses of SCLM include fibroids, persistent insect bite granulomas and cancers, among others. This patient’s tumour appeared at the surgical incision site, thus being misdiagnosed as a keloid. The most frequent symptom of SCLM is pain (80–95%), and other common symptoms include itching, feeling of heat and bleeding.³ The patient in this case had no obvious symptoms or only mild itching, which was also a factor leading to misdiagnosis.

Although surgical removal is the most effective treatment for this disease, there is still a relatively high rate of recurrence following the surgery.² As shown by histopathology, the patient’s tumour invaded the subcutaneous adipose layer. However, chest computed tomography (CT) and abdominal ultrasound indicated that there was no tumour metastasis. To prevent a recurrence, this patient underwent expanded resection with Mohs micrographic surgery, and no recurrence has been observed so far. For primary SCLM, wide local excision, and Mohs micrographic surgery in particular, have been confirmed to be effective and recommended.^1,4,5 The tumour is likely to recur due to incomplete resection. After undergoing R0 resection with 1 cm safety margins, the rate of local recurrence for SCLM is extremely low, and the occurrence of metastasis is rare.^4,5 This patient experienced recurrence twice, mainly because there was no clear diagnosis in the past, which did not attract sufficient attention from the doctors and the patient. After a definite diagnosis, we suggested the patient undergo further extensive excision using the Mohs micrographic surgery; the patient has not experienced any recurrence during a 2-year follow-up. Follow-up is recommended to be conducted every six months for SCLM within the first two years after surgery.⁴

In this case, we aim to draw attention to two key points. First, SCLM is prone to misdiagnosis and missed diagnosis. Histopathology and immunohistochemistry (IHC) are invaluable tools for accurate diagnosis. Second, in the treatment of SCLM, wide local excision, especially Mohs micrographic surgery, is highly recommended to minimise the risk of recurrence.