Molecular genetic analysis excludes implantation metastasis of basal cell carcinomas

Basal cell carcinoma (BCC) of the skin is the most common tumor in the white population. A 66-year-old man developed 2 BCCs at the left parietal region of the head and at the helix of the left ear. The 2 lesions matched exactly when pressing the ear against the head, suggesting an implantation metastasis mechanism. Molecular genetic techniques were used to confirm or exclude such a mechanism in this rare clinical constellation. Tumor tissues were precisely microdissected for DNA isolation. Exons 5-9 of the p53 tumor suppressor gene were directly sequenced. In addition, loss of heterozygosity analysis of chromosome 9q was performed using 5 polymorphic microsatellite markers. The BCC of the ear revealed a p53 mutation at codon 273, whereas the other one lacked this mutation. In addition, the smaller BCC of the ear showed loss of heterozygosity at 9q33.3, in contrast with the larger BCC. Interestingly, histologically normal skin of the ear distant from the small BCC had the same deletion, indicating a field defect of this skin patch at 9q33.3. Molecular genetic analysis clearly demonstrated different genetic alterations of the two BCCs and therefore most likely excludes a mechanism of implantation metastasis.