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Linear epidermal nevi are believed to be caused by an autosomal dominant lethal mutation that can only be expressed by mosaicism. Becker's nevus can be explained by paradominant inheritance which is only manifested clinically by an acquired loss of heterozygosity. We present the case of a 16-year-old female with an epidermal nevus located on the left side of the neck, and also a Becker's nevus located on the ipsilateral shoulder. It is interesting to speculate that this supposed double mosaicism could be another example of "twin spotting" or non-allelic didymosis, although the possibility that this is a chance association cannot be ruled out, as the lesions are not closely associated.

Five cases of a distinctive tumor located in the soft tissues of the lower neck in adults are described. The lesion is characterized microscopically by the presence of four components: cellular areas made up of spindle elements; epithelial islands composed of solid nests, trabeculae and cysts; mature adipose tissue; and lymphocytes, sometimes arranged in a Hassall's corpuscle-like fashion. Electron microscopy and immunostaining for keratin showed that the spindle cell component was of epithelial nature. These tumors were supraclavicular or suprasternal in location, and no local recurrence has developed in any case following local resection. We interpret these lesions as benign tumors arising on the basis of a developmental defect. We think that they are derived from the third branchial arch and that they are composed of abnormal thymic tissue.