Internal malignancies infrequently metastasize to the skin. Skin metastases may be the first presentation of underlying internal malignancy and are easily accessible sites for biopsy and diagnosis. If concurrent internal malignancy is found, skin metastases may represent advanced or progressive cancer and can alter treatment decisions.
Cutaneous metastasis from internal malignancy is a critical diagnosis for a dermatologist to consider.
Cutaneous lesions are accessible sites for biopsy to allow for a diagnosis and appropriate staging and to guide potential treatment decisions.
The highly variable, nonspecific, and often subtle appearance of malignant skin metastases make the diagnosis challenging.
Cutaneous metastases are most likely to appear on the head, neck, and trunk and less commonly present on limbs.
PATIENT EDUCATION POINTS
Internal malignancies metastasize to the skin relatively infrequently. Among all skin tumors, they represent a small minority of only 2%.1 Clinical presentations are polymorphous and nonspecific and often mimic benign and common entities, thus making the diagnosis often challenging. Skin metastases may be the first presentation of underlying internal malignancy, and they are easily accessible sites for biopsy and diagnosis by the dermatologist and pathologist. At the time of diagnosis of a cutaneous metastasis, the primary internal malignancy is often at an advanced stage, and this finding may influence overall treatment decisions and guide appropriate staging.
Cutaneous metastasis from internal malignancy is a relatively uncommon yet critical diagnosis for the dermatologist to consider. Quick identification of such lesions is important because they can be the first sign of internal malignancy (1% of cases) or the first sign of extranodal metastasis (7.6% of cases).2,3 The incidence of cutaneous involvement in the setting of metastatic disease ranges from 0.6% to 10%, as reported in the literature.3 This wide incidence range can be attributed to the various inclusion and exclusion criteria for cutaneous metastases, as some studies, for example, have excluded those metastases that originate from hematologic malignancies or melanoma or by direct extension.4
Primary malignancies have different tendencies for metastasis to the skin. It has been reported that as many as 45% of patients with metastatic melanoma, 30% of patients with metastatic breast cancer, and 13% of patients with metastatic squamous cell carcinoma of the head and neck develop cutaneous metastases.3 In comparison, less than 3% of patients with metastatic lung, stomach, pancreatic, uterine cervix, prostate, or testicular cancer are reported to develop cutaneous metastases.3 In women, breast cancer is the largest source of cutaneous metastases (71%), followed by melanoma (12%), ovarian cancer (3.3%), and cancers of the oral cavity (2.3%).3 In men, melanoma is the largest ...