๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Blue nevus-like metastatic melanoma
Blue nevus-like metastatic melanoma
Blue nevus-like metastatic melanoma is rare but represents a very serious source of misdiagnosis.1โ3 One or multiple lesions may be seen and they usually, but not always, develop at sites close to the primary tumor. Very rarely, lesions may be distant. They resemble a blue nevus clinically and histologically. They are often small and microscopically are characterized by dendritic, deeply pigmented melanocytes. Cytological atypia can be very subtle and this is further compounded by the prominent pigmentation (Fig. 26.97). Bleaching can therefore be useful. Resemblance to ordinary blue nevus or epithelioid blue nevus may be seen. Clues to the diagnosis of malignancy reside in the presence of cytological atypia, mitotic figures, and inflammation mainly at the periphery of the lesion. Histologic diagnosis is extremely difficult and close clinicopathological correlation is crucial.
Cytogenetic studies by FISH may be of help in establishing the distinction. In a study comparing epithelioid blue nevi with blue nevus-like cutaneous metastasis, it was shown that most of the latter had important copy number changes in chromosomes 6p25, 11q13, and centromere 6 while the former lacked cytogenetic changes.2 Uveal melanoma can also give rise to blue nevus-like melanoma which can be detected by detection of genetic events such as monosomy for chromosome 3 resulting in loss of BAP1.4 Detection of the GNAS or GNA11 mutation of uveal melanoma is not helpful alone in this context since these mutations can also be seen in blue nevi.
Fig. 26.97 Blue nevus-like metastatic melanoma: (A) at low-power examination, the features could easily be mistaken for a common blue nevus; (B) in addition to pigment-laden melanophages and dendritic cells, there are scattered melanoma cells. Note the multinucleate form with vesicular nuclei and prominent nucleoli. The patient had a melanoma previously excised at this site.