CLM are very rare tumours. They typically present with skin changes such as discolouration and ulceration, and are generally small at presentation (1–2
cm). Due to their low incidence and atypical presentation, they are often misdiagnosed. The most effective treatment of CLM is wide excision with a 3-5-cm lateral margin and a depth that includes the subcutaneous tissue and fascia [3
]. Local excision without adequate margins leads to recurrence, and increases the risk for metastatic and possibly fatal disease.
Leiomyosarcoma of the skin can be classified as either superficial (cutaneous or subcutaneous) or metastatic leiomyosarcoma from a distant visceral site such as the uterus or retroperitoneum [2
]. Differentiation between the cutaneous and subcutaneous subtypes is not always straightforward, and the distinction is made on the basis of different histological features and biological behaviour [5
]. As in our patient, CLM occurs most often on the extremities [6
]. The metastatic potential differs significantly between the histological subtypes, with the cutaneous variant having a very low rate of distant metastasis and a local recurrence rate of 30% [3
]. In this specific case, it also concerned a CLM and, because of the clear surgical margins, has an excellent prognosis.
The aetiology of these tumours is relatively unknown, although antecedent traumatic injury, ionising irradiation, chemicals, sunlight and lupus vulgaris have been associated with this type of tumour [7
]. We here describe the first patient with CLM arising in a small pox scar. There are various reports on CLM with a similar association with scars [7
]. The most common association, however, is found in burn scars. The pathogenesis of malignant transformation in burn scars is not known, mainly because of the low incidence with only 11 cases reported in the literature [9
Besides the occasional occurrence of CLM, a familial occurrence of cutaneous leiomyosarcoma with renal cancer has been described in the context of hereditary cutaneous leiomyomatosis and renal cell cancer (HLRCC) [10
]. This rare inherited tumour syndrome is caused by germ line mutations in the fumarate hydratase (FH) gene [12
]. However, mutations in FH do not explain sporadic CLM formation in scar tissue, since aberrant FH expression or somatic mutations are not seen in sporadic tumours [13
]. Adjuvant therapies include radiation therapy, chemotherapy and super voltage cobalt therapy, although CLM has been reported to be both radio- and chemotherapy resistant. [15
Because this is the first report of a CLM arising in a small pox scar, the presence of a common pathway to malignant transformation with burn scars cannot be determined. Although only a few risk factors have been identified, the most obvious relation with scar tissue has to be the antecedent traumatic injury. The extended time interval between scarring and malignant changes makes it difficult to advise strict follow-up for patients with small pox scars. One should be aware however that atypical changes and/or symptoms occurring in a small pox scar could potentially mean malignant transformation, and adequate diagnostic procedures such as local biopsy and/or primary/secondary wide local excision are the first appropriate steps.