Activation of the PI3K/AKT signalling pathway in non-melanoma skin cancer is not mediated by oncogenic PIK3CA and AKT1 hotspot mutations.

Non-melanoma skin cancer represents the most frequent human cancer entity. Activation of the PI3K/AKT signalling pathway has been reported both in squamous cell carcinoma (SCC) of the skin and in basal cell carcinoma (BCC). In many cancers, including SCC of the head and neck, the oesophagus and the penis, activation of this pathway is mediated by oncogenic PIK3CA and AKT1 mutations. We therefore screened 61 non-melanoma skin cancer samples (30 SCC and 31 BCC) for the presence of activating PIK3CA and AKT1 mutations. PIK3CA hotspot mutations were analysed using a highly sensitive SNaPshot assay, and exon 4 of AKT1 was sequenced directly. In addition, immunohistochemistry was performed for phosphorylated AKT protein. Immunohistochemical expression of pAkt was observed both in SCC and in BCC samples, indicating an activation of the PI3K/AKT pathway. Although SCC showed higher expression levels than BCC, this difference was not significant. However, none of the 61 non-melanoma skin cancer samples revealed any PIK3CA and AKT1 hotspot mutations at the investigated loci. We conclude that PIK3CA and AKT1 hotspot mutations do not contribute to the activation of the PI3K/AKT signalling pathway in non-melanoma skin cancer. The distinct PIK3CA mutation spectrum between SCC of the skin and SCC of other tissues may reflect the different carcinogens which are involved into the mutagenesis of these cancers. PIK3CA and AKT1 hotspot mutations are obviously not caused by UV light exposure, the main risk factor in non-melanoma skin cancer.