Skin metastases (cutaneous metastases) occur when cancer spreads from a primary tumor site elsewhere in the body to the skin. The skin is a relatively uncommon destination for cancer, involving only a small percentage of patients with internal malignancies. When they appear, however, these lesions often signal that the underlying cancer is in an advanced stage. Recognizing these secondary tumors is important because they can occasionally be the first sign of an undiagnosed internal cancer.
Visual Characteristics of Individual Lesions
The most frequent presentation of a skin metastasis is a firm, round or oval nodule. These lumps are typically felt beneath the skin’s surface, in the dermis or subcutaneous fat, ranging in size from barely noticeable to several centimeters across. The texture is often described as rubbery or hard, and the nodule may be movable or fixed in place.
The color of these lesions is variable but commonly appears flesh-colored, pink, or red-purple. If the primary cancer is melanoma, the metastases may be pigmented, showing shades of brown, blue, or black. Sometimes, the lesions break down and form open sores, known as ulcerative lesions, which fail to heal.
Less common visual forms exist that mimic specific skin conditions. A lesion may present as a plaque, a flat, raised area that sometimes gives the skin an “orange peel” texture (peau d’orange). Another presentation is carcinoma erysipeloides, an inflammatory metastasis appearing as a sharply demarcated, warm, red plaque that closely resembles the bacterial skin infection erysipelas.
A rare but distinct form is carcinoma en cuirasse, where the affected skin becomes hardened, thickened, and leather-like due to extensive cancer cell infiltration. Some lesions may also appear as red patches with numerous tiny blood vessels, a form termed carcinoma telangiectoides. The appearance is highly dependent on the type of primary cancer and how it spreads into the skin layers.
Common Patterns of Distribution and Location
Skin metastases typically appear in a body region near the site of the primary internal tumor. For instance, lung and breast cancers often lead to skin metastases on the chest wall. Cancers originating in the gastrointestinal tract, such as colon or stomach cancer, frequently metastasize to the skin of the abdomen and pelvis.
A characteristic pattern for abdominal metastases is the Sister Mary Joseph nodule, a palpable mass found at the umbilicus (belly button). The scalp is also a common site for metastases, particularly from breast, lung, and kidney cancers, sometimes resulting in localized hair loss (alopecia neoplastica). Head and neck regions are generally frequent sites for distant metastases.
Beyond clustering near the primary site, the lesions can follow specific lines or paths. One pattern is zosteriform metastasis, where lesions arrange themselves along the path of a nerve, visually mimicking an outbreak of shingles (herpes zoster). Another is an inflammatory presentation, often seen with breast cancer, where the skin exhibits widespread redness and swelling, frequently affecting the chest wall.
The lesions can also appear in or near surgical scars, indicating spread through direct implantation during a procedure or via the lymphatic system. Lung cancers tend to favor supra-diaphragmatic (above the diaphragm) skin regions, while colorectal cancers often show a predilection for infra-diaphragmatic (below the diaphragm) areas.
How Skin Metastases Differ from Benign Skin Issues
Cutaneous metastases are difficult to distinguish from common benign skin conditions because of their highly variable appearance. They are often mistakenly identified as cysts, lipomas, benign moles, or inflammatory conditions like cellulitis or erysipelas. The key differentiator is often the speed and manner of their development.
Unlike most benign lesions, which remain stable, skin metastases frequently present as new, rapidly developing nodules. They tend to be firm or hard to the touch, which helps differentiate them from softer benign growths like lipomas or cysts. A nodule that appears suddenly and grows quickly without a clear cause is a significant warning sign.
Benign moles usually have symmetrical shapes, uniform color, and smooth borders. Conversely, a metastatic lesion may be asymmetrical, have irregular edges, and exhibit multiple or uneven colors, especially if originating from melanoma. Any existing skin lesion that begins to change in size, shape, color, or elevation should be evaluated by a healthcare professional.
While some benign lesions can be symptomatic, a skin metastasis may be asymptomatic or painless in its early stages, though pain or tenderness can develop later. The rapid onset of a firm, non-tender lump, particularly in an individual with a known history of cancer, should prompt immediate medical consultation.
Primary Cancers Associated with Skin Metastases
The appearance of a skin metastasis is often influenced by the original tumor’s cell type. The most common internal cancer to metastasize to the skin in women is breast cancer, followed by lung cancer and melanoma. In men, the most frequent sources are lung cancer, melanoma, and colon cancer.
Breast cancer metastases frequently present with inflammatory patterns or as hard, fibrotic plaques on the chest wall. Lung cancer lesions are often firm, red nodules found on the chest, abdomen, or back. Melanoma has the highest likelihood of spreading to the skin, often appearing as blue or black nodules that may resemble a common mole.
Kidney cancers (renal cell carcinoma) can produce metastases notable for their deep purple or highly vascular appearance. Colorectal cancer metastases commonly present as nodules on the abdomen or pelvis, sometimes manifesting as the umbilical Sister Mary Joseph nodule. This variability underscores why a definitive diagnosis requires a biopsy and tissue examination.