Mechanisms of metastasis.

The role of dermatologists in the diagnosis and treatment of skin cancer continues to increase. Consequently, they will more frequently be involved in the diagnosis, treatment, and management of patients with metastatic or potentially metastatic tumors. Squamous cell carcinomas and malignant melanomas are frequently seen in dermatologic practices and have the capability to metastasize. Metastases are the result of a complex process that is characterized by a sequence of steps, each of which requires acquisition by the malignant cell of key biologic properties. The metastatic sequence can be conceptualized as detachment from the primary tumor followed by invasion, intravasation into a vessel, circulation, stasis within a vessel, extravasation, invasion of the recipient tissue bed, and ultimately proliferation. The basic steps of the metastatic sequence are described as well as how these steps and other tumor cell adaptations can affect the clinical patterns of metastasis. Finally, practical applications of the understanding of these principles of metastasis are discussed.