Cutaneous metastases

Epidemiology & commonest primaries

• Overall incidence in cancer patients: 0.7–9%; rises with stage IV disease.
• Women — breast carcinoma (~70% of cutaneous metastases in women); melanoma; ovarian; lung.
• Men — per Lookingbill 1993, melanoma is the commonest primary cutaneous metastasis (~32%), followed by lung carcinoma (~12%), colorectal (~11%); head & neck SCC and renal cell carcinoma also reported.
• Cutaneous deposits as the first sign of malignancy occur in 0.5–1% — most commonly lung and renal cell carcinomas.

Clinical patterns

• Solitary or multiple nodules — most common; firm, painless, dermal/subcutaneous, often mistaken for cysts or lipomas.
• Sister Mary Joseph nodule — umbilical metastasis; classically gastric, pancreatic, colorectal or ovarian primary; signifies poor prognosis.
• Carcinoma erysipeloides — well-demarcated red plaque mimicking erysipelas/cellulitis; classically breast cancer to chest wall via dermal lymphatics.
• Carcinoma en cuirasse — diffuse sclerotic infiltration of the chest wall; classical late breast carcinoma.
• Carcinoma telangiectoides — telangiectatic vascular plaques; breast and lung primaries.
• Alopecia neoplastica — scarring alopecic plaques on the scalp from breast and other primaries.
• Zosteriform metastases — dermatomal cutaneous deposits mimicking shingles.

Diagnosis

• Punch or excisional biopsy with adequate dermal/subcutaneous sample.
• Immunohistochemistry to characterise primary site:
  • Breast — ER, PR, HER2, GATA3, mammaglobin.
  • Lung — TTF-1, napsin A (adenocarcinoma); p40, p63 (squamous).
  • Colorectal — CK20+, CDX2+, CK7−.
  • Renal cell — PAX8+, RCC marker, vimentin.
  • Ovarian — PAX8+, WT1+, CA-125.
  • Prostate — PSA, NKX3.1.
  • Melanoma — S100, SOX10, Melan-A, HMB-45.
• Imaging staging (CT chest/abdomen/pelvis ± PET-CT) when no known primary.

Management

• Primary disease driven — refer to or coordinate with the appropriate oncology team.
• Local options for symptomatic / single lesions:
  • Excision for solitary, accessible, painful or bleeding lesions.
  • Palliative external beam radiotherapy.
  • Electrochemotherapy (NICE IPG446 for skin metastases from non-skin primary tumours and melanoma) — bleomycin + electroporation; useful for multiple superficial metastases especially breast (see monograph).
  • Topical therapies (miltefosine, imiquimod) for superficial breast metastases.
  • Intralesional chemotherapy or T-VEC (in melanoma).
• Systemic therapy of the primary tumour (chemotherapy, hormone therapy, targeted therapy, immunotherapy) addresses the underlying disease.

Prognosis

Cutaneous metastases generally indicate stage IV disease and a guarded prognosis — median survival 6–12 months, depending on primary tumour biology and response to systemic therapy. Some primaries (e.g. breast cancer with HER2-targeted therapy, melanoma with checkpoint inhibitors) have substantially better outcomes today than historically. Early biopsy of any suspicious cutaneous lesion in a known cancer patient — or a previously well patient with constitutional symptoms — is the most important diagnostic step.