Dermoscopic and histopathological findings of polymorphous vessels in amelanotic cutaneous metastasis of pigmented cutaneous melanoma

Conflicts of interest: none declared. Sir, An 85‐year‐old Japanese man presented with primary malignant melanoma, a 30 mm black ulcerative plaque, on his right forefinger. Total amputation of the right forefinger was performed in August 2004 (tumour thickness 6 mm; stage IV). After the operation, a local injection of interferon beta (300 × 104 IU) was given once monthly. In April 2006, multiple skin metastases developed. A nonpigmented red ulcerative nodule, 7 mm in diameter, was detected on his right upper back. Based on the dermoscopic findings of polymorphous vessels, including linear irregular vessels, dotted vessels and glomerular vessels (Fig. 1), the lesion was suspected to be cutaneous metastasis of melanoma. Histopathological findings of the lesion are shown in Figure 2a,b. The histopathological and the dermoscopic vascular structures were taken to be the same because both were located in the superficial and peripheral portions of the lesion. Histopathologically, the spindle cells lining the vascular structures were not atypical and the basal membrane of the structures was positive on Alcian blue–periodic acid–Schiff (AB‐PAS) staining. Immunohistochemical studies showed that the spindle cells were positive for CD34 and vimentin (Fig. 2c–e). In contrast, atypical melanocytes in the dermis were negative for AB‐PAS staining and for CD34, but positive for HMB‐45 and vimentin. These results confirmed that the lesion was a cutaneous metastasis of melanoma, and that the vascular structures were composed not of melanoma cells but of endothelial cells.