Increased tissue mucin is occasionally seen in malignant melanomas, particularly in desmoplastic melanomas. Usually this is not conspicuous. There are melanomas, primary or metastatic, within which tissue mucin may become very prominent, and such melanomas are designated as myxoid malignant melanomas or mucinous malignant melanomas.

Myxoid malignant melanomas are very rare. It is important to be aware of the existence of such melanomas because of the difficult differential diagnosis invoked when one of these is encountered.

Evidence of the radial growth phase of a melanoma combined with S-100 positivity and a negative keratin reaction are diagnostic in a primary lesion. The diagnosis in a metastatic lesion depends on a clinical history of a primary melanoma, which is not necessarily mucinous, combined with immunoperoxidase studies that rule out other possibilities and point towards a diagnosis of malignant melanoma.

	Low power view of left part of lesion.
	High power of above showing the dermoepidermal junction. This shows part of the radial growth component of the melanoma.
	Low power view of area to the right of above.
	High power view of above. These cells are S-100 positive, and negative for keratin.

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