Cutaneous metastases

The skin is a relatively uncommon site for metastases, compared with other organs such as the liver, lung and bone. Skin metastases can result from spread from an internal cancer or a skin cancer, usually melanoma. In most cases cutaneous metastases develop after the initial diagnosis of the primary malignancy, and late in the course of the disease. In very rare cases, skin metastases may occur at the same time or before the primary cancer has been diagnosed and may be the prompt for further thorough investigation.

This chapter is set out as follows: 

• In a generally accepted order of frequency, the breast, skin (melanoma), lung, colon, stomach, upper aerodigestive tract (nasal sinuses, larynx, oral cavity), kidney and uterus are the most frequent organs to produce cutaneous metastases

• The most common skin metastases from a previously unknown primary tumour originate from the kidney, lung, thyroid and ovary

• Although asymptomatic in most instances, pain and tenderness may be noted

Distribution

• Most cutaneous metastases occur in a body region near the primary tumour
• Common cutaneous sites for metastases and their probable primary sites are as follows:
  • Scalp - breast, lung, kidney
  • Face - oral squamous cell carcinoma, lung, kidney 
  • Neck - oral squamous cell carcinoma
  • Chest - breast, lung, melanoma
  • Back - lung
  • Abdomen - colon, lung, stomach, breast, ovary
  • Umbilicus (Sister Mary Joseph's nodule) - stomach, colon, ovary, kidney, breast
  • Pelvis - colon
  • Extremities - melanoma, breast, lung, renal, intestinal 

Morphology 

• Patients may present with a rapidly developing nodule or subcutaneous nodule
• Lesions can be single or multiple
• Nodules are often round or oval, firm, mobile and rubbery in texture
• The nodules are usually flesh coloured, although they may be red-purple, brown or blue-black

Breast cancer is the most common internal malignancy to spread to the skin. In addition to metastatic spread, it can also spread directly to the skin where it can present in a number of ways:

• Non-specific inflammation and tumid ulceration
• Carcinoma erysipeloides - a very marked inflammatory reaction without pyrexia
• Carcinoma en cuirasse - this may have an early inflammatory response, but at a later stage develops a morphoea-like sclerotic pattern
• Peau d'orange - an orange peel-like appearance
• Carcinoma telangiectoides - telangiectatic changes
• Most of the changes referred to above occur in the vicinity of the primary tumour as a result of direct spread into the skin, but can occasionally occur at distant sites following metastatic spread, including to areas of scar tissue and the scalp (alopecia neoplastica)
• Although these phenomena are most commonly reported with breast cancer, they can arise with other internal malignancies