<i>PIK3CA</i> hotspot mutations in Merkel cell carcinoma.

<p>(a) The heterozygous p.E542K (c.G1624A) <i>PIK3CA</i> hotspot mutation was detected in sample no. 27 by direct sequencing (left) and a <i>PIK3CA</i> SNaPshot® assay (right) covering the most frequent hotspot <i>PIK3CA</i> mutations. The number of the wildtype codons is indicated above the peaks in the SNaPshot® assay. In brief, the SNaPshot® assay comprises a multiplex PCR for exons 9 and 20 of <i>PIK3CA</i>, followed by extension of 4 primers specific for the most frequent <i>PIK3CA</i> hotspot mutation loci. Because fluorescent dideoxynucleotides are used for this primer extension step, only one peak appears at the base position with the potential mutation. The color of the peak allows discrimination of wildtype and mutated alleles. (b) The heterozygous p.E545Q (c.G1633C) <i>PIK3CA</i> hotspot mutation was detected in sample no. 24 by direct sequencing (left) and a <i>PIK3CA</i> SNaPshot® assay (right) covering the most frequent hotspot <i>PIK3CA</i> mutations. The number of the respective wildtype codon is indicated above the peaks in the SNaPshot® assay.