A malignant chondroid syringoma (also known as a "malignant mixed tumour" or "MCS" ) is a very uncommon cutaneous (skin) condition characterised by an adnexal eccrine tumour.
It is commonly reported to present on the trunk and extremities and behave in an aggressive manner. MCS is a cancerous subtype of its benign counterpart, chondroid syringoma, and is the least common variation that has an approximated prevalence of less than 0.005%. These tumours mainly arise "from sebaceous glands, sweat glands, and ectopic salivary glands" (Tural, Selçukbiricik, Günver, Karışmaz, and Serdengecti, 2013) and are rarely encountered in radiopathological and clinical practice. The tumours commonly appear with an asymptomatic "slow-growing, painless, solid subcutaneous or intradermal nodules with a normal margin" (Obaidat, Alsaad, and Ghazarian, 2007) and make up for less than one percent of all primary skin tumours. Commonly appearing in the limbs and body, these asymmetrical tumours range from two millimetres to more than three centimetres. MCS is one of the rarest subtypes of tumours and usually requires aggressive surgery to terminate. Despite accounting for only a small number of tumours recorded each year, malignant mixed tumours are easily confused with other skin conditions (such as epidermal cyst, pilar cyst, calcifying epithelioma, or a solitary trichoepithelioma (Tural, Selçukbiricik, Günver, Karışmaz, and Serdengecti, 2013)) and have high potential for recurrence after surgical excision. The aggressiveness of malignant chondroid syringoma varies, as 49% of cases have had local recurrence whereas some demonstrate regional lymph node or osseous metastasis. The rare neoplasms generally do not follow a determinate development path and are often difficult to diagnose.
Histologically, these malignant mixed tumours have epithelial and mesenchymal components and are very large, nodular, circumscribed, and nonulcerated. They are morphologically identical to pleomorphic adenoma and have a female predilection. They range from developing deep dermal to subcutaneous nodules and metastasise at a very high rate. Malignant mixed tumours can emerge "de nova or more rarely develop from a cartilaginous syringoma."(IADVL, 2004)
Causes
Currently malignant mixed tumours do not have a definitive predisposing factor; however, prior physical injury has been proposed as a potential risk for the emergence of these tumours. Chondroid syringoma less than three centimetres are shown to have a heightened risk of malignancy. Other critical indicators include excessive mucoid matrix, – a connective tissue tumour with a myxoid background that is composed of "clear, mucoid substance – numerous mitoses, and poorly differentiated chondroid components." (Metzler, Schaumburg-Lever, Hornstein, and Rassner, 1996)
Diagnosis
Diagnosing malignant mixed tumours is difficult as there many types of tumours and their variants. Malignant chondroid syringoma is particularly challenging to distinguish from other skin tumours as it is prone to the absence of definitive symptoms and an ambiguous clinical presentation. Some signs that help determine diagnosis of malignancy include: "mitosis, nuclear atypia, pleomorphism, lymphatic invasion, and local recurrence" (IADVL, 2004). Though it is usually found within women in the forties, the youngest-recorded case was fourteen years old and the oldest was eighty-six. The tumour is described as invasive and is clinically characterised by faster growth than the benign chondroid syringoma. They can generally be diagnosed when presenting "an epithelial component, eccrine or apocrine differentiation and myoepithelial component of fluctuating prominence" (IADVL, 2004). Diagnosis is recommended to follow microscopic analysis to ensure correct examination.