How often do internal malignancies metastasize to the skin?

Cutaneous metastases of internal malignancies are relatively uncommon. An autopsy study including 7500 patients with internal malignancies demonstrated cutaneous metastases in 9% of patients. Most cases occur late in the course of the disease, but cutaneous metastasis may also be the initial presentation of an internal malignancy.

Lookingbill DP, Spangler N, Helm KF: Cutaneous metastases in patients with metastatic carcinoma: a retrospective study of 4020 patients, J Am Acad Dermatol 29:228–236, 1993.