CUTANEOUS MALIGNANT MELANOTIC NEUROCRISTIC TUMORS ARISING IN NEUROCRISTIC HAMARTOMAS - A MELANOCYTIC TUMOR MORPHOLOGICALLY AND BIOLOGICALLYDISTINCT FROM COMMON MELANOMA

Cutaneous neurocristic hamartomas (CNH) are pigmented lesions of neura l crest origin that involve the skin and superficial soft tissue. They consist of a complex proliferation of nevomelanocytes, schwann cells, and pigmented dendritic and spindled cells. Malignancies can arise wi thin these lesions, but few studies have dealt with this issue. We stu died seven cases of CNH in which malignancy supervened. They included four congenital and three acquired lesions that involved the head and neck (five cases) or back (two cases) in patients aged from Il to 67 ( mean, 32) years. Malignant tumors developed 15 to 67 (mean, 32) years after identification of the pigmented lesion in the congenital CNH and after 1 to 6 (mean 3.5) years in the acquired CNH. The malignant tumo rs had a deep intradermal or subcutaneous origin and lacked a junction al component. Most were circumscribed, multinodular, melanin-containin g tumors composed of bland, small, rounded to spindled cells, focally displaying a trabecular or nested growth pattern. Nuclear palisading a nd perivascular pseudorosettes were present in several tumors. In two examples, the neoplasm consisted predominantly of large pleomorphic ep ithelioid cells. Tumors contained immunoreactive S-100 protein (all of seven cases), a melanoma-associated antigen (HMB-45) (five of six cas es), neuron-specific enolase (five of seven cases) and vimentin (six o f six cases). The four patients with congenital lesions tended to have multiple recurrences and died of disease after 2 to 20 (mean, 9) year s, three with metastases, one with direct invasion of the posterior fo ssa. The three patients with acquired lesions are alive after 1 to 5 y ears, two with persistent disease. In contrast to common melanomas, th ese tumors have a propensity to recur as bulky nodules and to metastas ize after many years or decades. Because these tumors exhibit melanocy tic differentiation and arise in hamartomatous lesions composed of neu ral crest derivatives, we have designated them cutaneous malignant mel anotic neurocristic tumors.