Malignant Melanoma in situ of the Lower Lip

Abstract

Primary malignant melanoma in situ of the lower lip is exceedingly rare. Two Japanese patients with malignant melanoma in situ in the mucous membrane of the lower lip are presented. One case was an 31-year-old female, and the other was an 14-year-old boy. Micro-scopically, atypical melanocytes evidenced by prominence of nuclei and nucleoli were observed, which were distributed individually as well as occasionally in nests. Atypical mitosis were frequently found in both cases. Ultrastructural examination recovered from paraffin sections confirmed the presence of melanozomes in these atypical melanocytes. Immunohistochemically, positive reactivity with ras P21 monoclonal antibody was observed in these atypical melanocytes. These findings indicated that malignant melanoma in situ may occur in the mucous membrane of the lower lip in rather younger generation.