When primary cancer spreads to the skin.

The lesions usually are asymptomatic, rapidly growing nodules that seem to crop up overnight. In most patients, the site is not far away from the primary tumor. For example, the metastatic seeds from breast carcinoma--the most common cause of secondary skin cancer--have an affinity for the anterior chest wall. An exception to this tendency toward localization is the scalp, which holds an odd attraction for implants from distant as well as nearby tumors. A high index of suspicion and an adequate biopsy are essential to diagnosis. The skin lesions can be puzzling when the primary tumor is silent or unrecognized. Tumors that masquerade as benign growths can allow a covert malignancy to remain undetected for a long time unless histologic sections are examined. Most secondary skin lesions do not require treatment. The exceptions are inflammatory, painful, or ulcerating neoplasms and relatively slow-growing tumors that yield to simple measures--i.e., surgical excision and/or radiotherapy. The psychologic value of treating symptom-free but highly noticeable lesions should also be considered.