Collision of desmoplastic-neurotropic melanoma and squamous cell carcinoma on the lip.

We report on a case of the collision of a desmoplastic-neurotropic melanoma and a squamous cell carcinoma on the lip. A 46-year-old male developed a multifocal infiltrative squamous cell carcinoma of the lower lip, which also showed sparse melanocyte atypia within the epidermis and an extensive spindle cell proliferation within the dermis, subcutaneous tissues and nerves. An immunohistochemical panel showed that the spindle cells were melanocytes, not derived from the squamous cell carcinoma. Double labeling with AE1/AE3 and S100 showed striking localized proximity of the spindle-cell melanocytic and keratinocyte components in some areas of this tumor. To our knowledge, this is the first report of the collision of a squamous cell carcinoma and desmoplastic-neurotropic melanoma.