Cutaneous Metastases of Unusual Tumor Types: Retrospective Single-Institution Analysis and Literature Review

Cutaneous metastasis (CM) is a rare manifestation of internal malignancy. We analyzed the incidence, clinical features, and patterns of metastatic spread among 408 CMs from 15 primary sites, excluding skin, breast, lung, colorectum, and hematolymphoid primary sites, in a 34-year (1990-2024) single-institution retrospective review (88 cases) and literature review (320 cases). CMs from thyroid were most common in the single-institution review. A young median age was observed in patients with CMs from soft tissue (14 years) and bone (32 years) tumors. Male predilection was most observed in CMs from esophagus, mesothelium, and kidney. CMs from 9 of 15 primary sites favored the head and neck region. CMs most presented as solitary lesions from bile duct (72%), thyroid (69%), and pancreas (67%) primary sites. In total, 45% of CMs from the bile duct were due to catheter-related tumor seeding. The primary sites with the highest percentage of CMs at initial presentation were neuroendocrine (55%), esophagus (45%), and pancreas (40%). The time interval between primary cancer diagnosis and development of CM ranged from 0 to 429 months. The shortest median time interval was observed in CMs arising from pancreas (1 month) and esophagus (2 months), while the longest median time interval was observed in those from prostate (80 months) and kidney (46 months). In summary, CM may be the initial clinical presentation of underlying malignancy from uncommon primary sites and can exhibit distinctive patterns of cutaneous spread based on the primary cancer type and anatomic location.