FGFR3, PIK3CA and RAS mutations in benign lichenoid keratosis

Summary Background Benign lichenoid keratoses (BLKs) are solitary skin lesions which have been proposed to represent a regressive form of pre‐existent epidermal tumours such as solar lentigo or seborrhoeic keratosis. However, the genetic basis of BLK is unknown. Objectives FGFR3, PIK3CA and RAS mutations have been shown to be involved in the pathogenesis of seborrhoeic keratosis and solar lentigo. We thus investigated whether these mutations are also present in BLK. Methods After manual microdissection and DNA isolation, 52 BLKs were screened for FGFR3, PIK3CA and RAS hotspot mutations using SNaPshot® multiplex assays. Results We identified 6/52 (12%) FGFR3 mutations, 10/52 (19%) PIK3CA mutations, 6/52 (12%) HRAS mutations and 2/52 (4%) KRAS mutations. FGFR3 and RAS mutations were mutually exclusive. One BLK showed a simultaneous PIK3CA and HRAS mutation. In nine BLKs with a mutation, nonlesional control tissue from the epidermal margin and the dermal lymphocytic infiltrate were wild‐type, indicating that these mutations are somatic. To demonstrate that these findings are specific, 10 samples of lichen planus were analysed without evidence for FGFR3, PIK3CA or RAS mutations. Conclusions Our results indicate that FGFR3, PIK3CA and RAS mutations are present in approximately 50% of BLKs. These findings support the concept on the molecular genetic level that at least a proportion of BLKs represents regressive variants resulting from former benign epidermal tumours such as seborrhoeic keratosis and solar lentigo.