p14ARF hypermethylation is common but INK4a-ARF locus or p53 mutations are rare in Merkel cell carcinoma.

Although the exact molecular mechanisms of Merkel cell carcinoma (MCC) tumorigenesis are unknown, they likely involve complex genetic alterations and mutations similar to those seen in many other cancers. In this study, we obtained MCCs from 21 elderly patients (19 women, 2 men) and analyzed their DNA for mutation of exons of interest in several tumor-suppressor genes or oncogenes known to be frequently mutated in skin cancer: p53 (exons 4-8), Ras (exons 1 and 2), c-Kit (exon 11), and the INK4a-ARF locus (encoding p14 and p16) (exons 1 and 2). Direct sequence analysis revealed p53 mutations (that is, at codons 224, 234, and 294) in three tumors (14%) and p16INK4a mutations (that is, at codon 6) in one (5%). No mutations were detected in Ha-Ras, Ki-Ras, N-Ras, c-Kit, or p14ARF. On the other hand, methylation-specific PCR revealed methylation of p14ARF promoter DNA in eight of 19 analyzable tumor samples (42%) and p16INK4a promoter DNA in one of 19 analyzable tumor samples (5%). Together, these findings suggest that p14ARF silencing may be an important mechanism in MCC tumorigenesis, and thus a potential target for therapeutic intervention in this highly aggressive tumor type.