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erbB receptors contribute to tumor formation and progression. Variable expression of erbB1, erbB2, and erbB3 has been reported in nevi and melanomas; erbB4 has hardly been investigated. We examined the expression of all 4 erbB receptors in common and dysplastic nevi and melanomas. Formalin-fixed, paraffin-embedded tissues of 100 melanomas, 27 common nevi, and 23 dysplastic nevi were immunostained with antibodies against the 4 erbB receptors. erbB3 and erbB4 showed stronger positivity in nevi than in melanomas, and in common than in dysplastic nevi. Staining pattern was more orderly in nevi than in melanomas. Common nevi showed more prominent membranous staining for erbB3 than dysplastic nevi followed by melanomas. In melanomas, greater thickness was associated with more widespread erbB2 and erbB3 staining in the vertical than in the radial growth phase, and in the dermal than in the epidermal component. Higher mitotic counts were associated with more widespread and intense erbB2 expression in the vertical growth phase than in the radial growth phase and in the dermal than in the epidermal component. Melanomas with more widespread erbB2 staining had heavier lymphocytic infiltrates. erbB1 expression was negligible in all groups. erbB2, erbB3, and erbB4 are expressed in all subtypes of melanocytic lesions, but with quantitative and qualitative differences. Receptor expression seems to decrease and to become less mature and orderly with tumor progression. The complex patterns of erbB receptor expression in melanocytic lesions warrant further investigation.

Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin that is associated with a high incidence of recurrence and metastasis. The therapeutic arsenal for this malignancy is limited and once it spreads, there is no effective treatment. c-kit expression has been demonstrated previously in primary MCCs thus raising the possibility of treating MCCs with imatinib mesylate, the tyrosine kinase inhibitor that has shown promise in the management of c-kit expressing tumors. In this study we examine 25 additional primary MCCs and also 6 of their lymph node metastases. Formalin-fixed, paraffin-embedded tissues were stained immunohistochemically with an antibody directed against the KIT receptor. Percentage and intensity of staining were analyzed semiquantitatively using a three-tiered system. Twenty-one of the 25 (84%) primary tumors stained positively for KIT, of which 14 (67%) showed widespread positivity. Five of the 6 lymph nodes (83%) were similarly positive. High mitotic rate and vascular invasion in the primary tumors tended to be associated with prominent staining in the lymph node metastases. No association was found between c-kit expression and outcome. We confirm that the majority of primary MCCs express c-kit and further find that metastases are positive for the KIT receptor as well. Thus, c-kit expression may be an early event in the transformation of MCC, but not a marker for tumor progression.