Dermal primary malignant melanoma in congenital nevuscellular nevus

Malignant melanomas normally arise at the dermoepidermal junction. Developm ent of these tumours in deeper layers of the dermis without having contact with the junction is rare. A small congenital melanocytic nevus localized i n the region of the waist band was excised because of mechanical irritation ; it had not shown any changes over years. A thorough examination of the wh ole body did not give any clue to a malignant melanoma. Histologically a co mpound nevus with the typical architecture of a congenital melanocytic nevu s was found. In the deeper dermis there was an isolated nodule of extremely atypical melanocytes with minimal pigmentation of melanin. S100 antigen co uld be demonstrated throughout the whole tumour whereas HMB45 was only foun d at the dermoepidermal junction. There was no marking of the tumour cells with a pancytokeratin antibody. A histological relationship between the new tumour and a mixed tumour of the left testicle, which had been excised 3 y ears ago could be excluded. We did not find any metastases neither by image -aided methods nor by sentinel lymph node biopsy.