At the left shoulder of a 58-year-old male patient an asymmetric tumour with not clear border, with different colours and a diameter more than 5mm was visible. In the last three months this tumour grew clearly and changed also in structures and colours. He was skin type II, more than 100 small, non suspicious nevi, seborrheic keratosis and angiomas in clinic and dermoscopy (FotoFinder).

In dermoscopy an asymmetric tumour appeared with different differential structures: atypical network with bluish-grey veil, streaks in the lower part and in the centre a distinct hint of a regression area; also pseudohorncysts and comedo-like openings were distributed over the tumour. Light to dark brown, blue, grey and black colours were found. With the exception of the lower right lateral area the border was clear terminated (FotoFinder, 20fold magnification).

Histology
Seborrheic keratosis

Remarks
Both diagnoses were possible in this case: invasive melanoma or seborrhoic keratosis. If no clear diagnosis is possible in clinic and dermoscopy, an excision biopsy with histopathological examination is recommended.

References
Braga JC, Scope A, Klaz I, Mecca P, Spencer P, Marghoob AA (2008) Melanoma mimicking seborrheic keratosis: an error of perception precluding correct dermoscopic diagnosis. J Am Acad Dermatol 58: 875-880