Skin metastasis

What is skin metastasis?

Skin, or cutaneous, metastasis (plural ‘metastases’) refers to growth of cancer cells in the skin originating from an internal cancer. In most cases, cutaneous metastasis develops after the initial diagnosis of the primary internal malignancy (e.g. breast cancer, lung cancer) and late in the course of the disease. In very rare cases, skin metastasis may occur at the same time or before the primary cancer has been discovered and may be the prompt for further thorough investigation.

Skin metastasis may also occur from a skin cancer, usually melanoma. The original or ‘primary’ melanoma produces metastases or ‘secondary’ growths in surrounding or distant skin sites and other tissues such as the lungs or brain.

What causes skin metastasis?

Skin metastasis occurs when cancerous cells break away from the primary tumour and make their way to the skin through the blood circulation or lymphatic system. Most malignant tumours can produce skin metastasis, but some are more likely to do so than others. When the following cancers have metastasised, they have quite a high chance of affecting the skin.

• Melanoma – 45% chance of developing skin metastasis (but only 15 to 20% of melanomas metastasise, so the overall chance of a skin metastasis is about 7-10%)
• Breast cancer – 30%
• Nasal sinus cancers – 20%
• Cancer of the larynx – 16%
• Cancer of the oral cavity – 12%

The incidence of skin metastasis varies but is somewhere between 3-10% in patients with a primary malignant tumour.

The sex and age of an individual also appears to determine the frequency of skin metastasis in certain primary cancers. The reason for this is unknown.

Below lists the common internal cancers that cause skin metastasis in decreasing order of frequency according to sex and age group.

What are the signs and symptoms of skin metastasis?

Most skin metastasis occurs in a body region near the primary tumour. The first sign of skin metastasis is often the development of a firm, round or oval, mobile, non-painful nodule. The nodules are rubbery, firm or hard in texture and vary in size from barely noticeable lesions to large tumours. These may be skin coloured, red, or in the case of melanoma, blue or black. Sometimes multiple nodules appear rapidly. The skin metastases may break down and ulcerate through the skin. Specific patterns include:

• Carcinoma erysipeloides: sharply demarcated red patch due to local spread of primary cancer blocking lymphatic blood vessels in adjacent skin.
• En cuirasse or sclerodermoid carcinoma: indurated fibrous scar-like plaques due to cancer cells infiltrating collagen in the skin
• Carcinoma telangiectoides: red patches with numerous blood vessels (telngiectases) or lymphatic vessels (lymphangioma-like)

Depending on the location of the primary tumour, skin metastasis display certain characteristic features.

Skin metastases

Metastatic melanoma near excision site	Distant metastatic melanoma	Metastatic melanoma
Metastatic breast cancer	Metastatic breast cancer	Metastatic adenocarcinoma of unknown origin (carcinoma erysipeloides)

What is the treatment for skin metastasis?

The underlying primary tumour needs to be treated. However, in most cases where skin metastasis has occurred, the primary cancer is widespread and may be untreatable. In this case, palliative care is given and includes keeping lesions clean and dry. Debridement can be done if lesions bleed or crust. Other therapies that may be helpful include:

• Imiquimod cream – may lead to regression of metastasis in some cases of melanoma
• Liquid nitrogen cryotherapy
• Photodynamic therapy
• Excision
• Carbon dioxide laser therapy
• Pulsed dye laser therapy
• Intralesional chemotherapy and cytokines

In many cases, skin metastasis causes disfigurement and discomfort. Removal of skin lesions by simple excision may enhance the patient’s quality of life but has little effect on the final outcome that is dictated by the primary cancer.