Any internal cancer can spread to the skin. Skin lesions due to the spread of internal cancers are called "metastases". The tumours that most frequently give rise to skin metastases in Singapore include lung cancer, colorectal cancer and breast cancer. The presence of metastases in the skin usually means that the internal cancer has spread to other organs as well.
Certain sites appeared to be favoured by particular tumours although generalisations are not possible. For example, the scalp, face and neck are the commonest sites of metastases from breast, lung and oral cavity cancers. Metastases on the chest is most often from breast or lung cancer. The name "Sister Joseph's nodule" has been given to metastases on the navel from cancer in the abdomen, pelvis or breast.
Metastases in the skin may appear as single or multiple nodules. The nodules are usually firm or hard, fixed or mobile and non-tender. They often grow rapidly to 1 to 3 cm in diameter. The colour is variable and may be red, brown, blue, black or flesh coloured.
When cutaneous metastasis is suspected, a specimen of the lesion should be surgically removed (skin biopsy) to confirm the diagnosis. If cancerous metastasis is confirmed the patient should undergo investigation to determine the site of the internal cancers.
Treatment of the patient depends on the type of primary tumour, the degree of spread and the overall physical condition of the patient. Medical options for therapy include radiotherapy and chemotherapy.